Fluorinated copolymer having sulfonyl pendant groups and compositions and articles including the same

ABSTRACT

The copolymer includes divalent units represented by formula —[CF 2 —CF 2 ]—, divalent units represented by formula; and one or more divalent units independently represented by formula: The copolymer has an —SO 2 X equivalent weight in a range from 300 to 2000. A polymer electrolyte membrane that includes the copolymer and a membrane electrode assembly that includes such a polymer electrolyte membrane are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2018/051094, filed Sep. 14, 2018, which claims priority to U.S.Provisional Application Nos. 62/558,655 and 62/558,671, filed Sep. 14,2017, and 62/730,648, filed Sep. 13, 2018, the disclosures of which areincorporated by reference in their entirety herein.

BACKGROUND

Copolymers of tetrafluoroethylene and polyfluorovinyloxy monomersincluding sulfonyl fluoride pendant groups have been made. See, forexample, U.S. Pat. No. 3,282,875 (Connolly), U.S. Pat. No. 3,718,627(Grot), and U.S. Pat. No. 4,267,364 (Grot). Copolymers of fluorinatedolefins and polyfluoroallyloxy sulfonyl fluorides have been made. See,for example, U.S. Pat. No. 4,273,729 (Krespan) and U.S. Pat. No.8,227,139 (Watakabe), and International Pat. Appl. Pub. No. WO 00/24709(Farnham et al.). Hydrolysis of the sulfonyl fluoride of thesecopolymers to form an acid or acid salt provides ionic copolymers, whichare also called ionomers.

Certain recently disclosed ionomers are said to have high oxygenpermeability. See, for example, U.S. Pat. Appl. Pub. Nos. 2017/0183435(Ino), 2013/0253157 (Takami), 2013/0245219 (Perry), and 2013/0252134(Takami), and U.S. Pat. No. 8,470,943 (Watakabe).

SUMMARY

While ionomers made from tetrafluoroethylene and polyfluorovinyloxy orpolyfluoroallyloxy sulfonyl fluorides monomers are known, certain ofthese materials are highly crystalline and difficult to disperse incommon solvent (e.g., water and alcohol mixtures) at high solidpercentages (e.g., at least 20% solids). Achieving high percent solidsmay be particularly challenging when an ionomer of high equivalentweight is desired. A high solids percentage is useful for making thickermembranes for membrane electrode assemblies. While for some applicationsthin membranes are desirable (e.g., automotive membranes can be about 12micrometers thick), other applications require thicker membranes (e.g.,greater than 30 micrometers or greater than 50 micrometers). Increasingthickness by using higher percent solids is advantageous over amulti-pass process to build thickness. Furthermore, increasing thesolubility in common solvents can obviate the need for using highboiling solvents such as DMF or DMSO and allow for using lowermanufacturing temperatures during the manufacturing process of ionomermembranes. Operating at lower coating temperature for the membrane orelectrode catalyst particle help protect the overall article ofmanufacture.

Easy-to-process ionomers with low hydrogen permeation for membraneapplications in fuel cells or high oxygen permeation ionomers forelectrode applications are also difficult to achieve. Membrane electrodeassemblies useful in solid polymer electrolyte fuel cells includeelectrode catalyst layers including a catalyst (e.g., platinum) and anionomer. Since the catalysts (e.g., platinum) are typically expensive,decreasing the amount of catalyst can be desirable. For an ionomer usedin the electrode, high oxygen permeability is desirable to minimizeresistance. In the ionic catalyst layer, it is desirable to have a highoxygen permeability without lowering the ionic conductivity.

The copolymers of the present disclosure include longer chain orbranched vinyl ether or allyl ether monomer units in addition totetrafluoroethylene and sulfonyl group-containing monomer units.Inclusion of such vinyl and allyl ethers can lead to an improvedprocessability profile in common solvents by improving solubility.Inclusion of such monomer units can also typically provide low hydrogenpermeation for membrane applications in fuel cells or high oxygenpermeation ionomers for electrode applications.

In one aspect, the present disclosure provides a copolymer includingdivalent units represented by formula [CF₂—CF₂]—, divalent unitsindependently represented by formula:

and one or more divalent units independently represented by formula:

In these formulas, a is 0 or 1, b is a number from 2 to 8, c is a numberfrom 0 to 2, and e is a number from 1 to 8. In each —SO₂X, X isindependently F, —NZH, —NZSO₂(CF₂)₁₋₆SO₂X′,—NZ[SO₂(CF₂)_(d)SO₂NZ]₁₋₁₀SO₂(CF₂)_(d)SO₂X′, or —OZ, wherein each Z isindependently a hydrogen, alkyl having up to four carbon atoms, analkali-metal cation, or a quaternary ammonium cation, X′ isindependently —NZH or —OZ, each d is independently 1 to 6, Rf is alinear or branched perfluoroalkyl group having from 1 to 8 carbon atomsand optionally interrupted by one or more —O— groups, z is 1 or 2, eachn is independently from 1, 3, or 4, m and m′ are each independently 0 or1, and Rf₁ is a branched perfluoroalkyl group having from 3 to 8 carbonatoms, with the proviso that if z is 2, one n may also be 2, with thefurther proviso that if a is 1, n may also be 2, and with the furtherproviso that when m′ is 1, Rf₁ is a branched perfluoroalkyl group havingfrom 3 to 8 carbon atoms or a linear perfluoroalkyl group having 5 to 8carbon atoms. The copolymer has an —SO₂X equivalent weight in a rangefrom 300 to 2000. In some embodiments, X is independently F, —NZH, or—OZ, wherein each Z is independently a hydrogen, alkyl having up to fourcarbon atoms, an alkali-metal cation, or a quaternary ammonium cation.

In another aspect, the present disclosure provides a copolymer includingdivalent units represented by formula —[CF₂—CF₂]—; divalent unitsindependently represented by formula:

and one or more other fluorinated divalent units independentlyrepresented by formula:

In these formulas, a is 0 or 1, b is 2 to 8, c is 0 to 2, e is 1 to 8,and each X′″ is independently —NZH, —NZSO₂(CF₂)₁₋₆SO₂X′, or—NZ[SO₂(CF₂)_(d)SO₂NZ]₁₋₁₀SO₂(CF₂)_(d)SO₂X′, wherein Z is a hydrogen,alkyl having up to four carbon atoms, an alkali-metal cation or aquaternary ammonium cation, X′ is independently —NZH or —OZ, each d isindependently 1 to 6, Rf is a linear or branched perfluoroalkyl grouphaving from 1 to 8 carbon atoms and optionally interrupted by one ormore —O— groups, z is 1 or 2, each n is independently from 1 to 4, m is0 or 1, m′ is 0 or 1, and Rf₁ is a branched perfluoroalkyl group havingfrom 3 to 8 carbon atoms, with the proviso that when m′ is 1, Rf₁ is abranched perfluoroalkyl group having from 3 to 8 carbon atoms or alinear perfluoroalkyl group having 5 to 8 carbon atoms The copolymer hasan —SO₂X′″ equivalent weight in a range from 300 to 2000.

In another aspect, the present disclosure provides a polymer electrolytemembrane that includes the copolymer of the present disclosure.

In another aspect, the present disclosure provides a catalyst ink thatincludes the copolymer of the present disclosure.

In another aspect, the present disclosure provides a membrane electrodeassembly that includes at least one of such a polymer electrolytemembrane or catalyst ink.

In another aspect, the present disclosure provides a binder for anelectrochemical system that includes the copolymer of the presentdisclosure.

In another aspect, the present disclosure provides a battery orelectrode that includes such a binder.

In this application:

Terms such as “a”, “an” and “the” are not intended to refer to only asingular entity but include the general class of which a specificexample may be used for illustration. The terms “a”, “an”, and “the” areused interchangeably with the term “at least one”.

The phrase “comprises at least one of” followed by a list refers tocomprising any one of the items in the list and any combination of twoor more items in the list. The phrase “at least one of” followed by alist refers to any one of the items in the list or any combination oftwo or more items in the list.

“Alkyl group” and the prefix “alk-” are inclusive of both straight chainand branched chain groups and of cyclic groups. Unless otherwisespecified, alkyl groups herein have up to 20 carbon atoms. Cyclic groupscan be monocyclic or polycyclic and, in some embodiments, have from 3 to10 ring carbon atoms.

The terms “aryl” and “arylene” as used herein include carbocyclicaromatic rings or ring systems, for example, having 1, 2, or 3 rings andoptionally containing at least one heteroatom (e.g., O, S, or N) in thering optionally substituted by up to five substituents including one ormore alkyl groups having up to 4 carbon atoms (e.g., methyl or ethyl),alkoxy having up to 4 carbon atoms, halo (i.e., fluoro, chloro, bromo oriodo), hydroxy, or nitro groups. Examples of aryl groups include phenyl,naphthyl, biphenyl, fluorenyl as well as furyl, thienyl, pyridyl,quinolinyl, isoquinolinyl, indolyl, isoindolyl, triazolyl, pyrrolyl,tetrazolyl, imidazolyl, pyrazolyl, oxazolyl, and thiazolyl.

“Alkylene” is the multivalent (e.g., divalent or trivalent) form of the“alkyl” groups defined above. “Arylene” is the multivalent (e.g.,divalent or trivalent) form of the “aryl” groups defined above.

“Arylalkylene” refers to an “alkylene” moiety to which an aryl group isattached. “Alkylarylene” refers to an “arylene” moiety to which an alkylgroup is attached.

The terms “perfluoro” and “perfluorinated” refer to groups in which allC—H bonds are replaced by C—F bonds.

The phrase “interrupted by at least one —O— group”, for example, withregard to a perfluoroalkyl or perfluoroalkylene group refers to havingpart of the perfluoroalkyl or perfluoroalkylene on both sides of the —O—group. For example, —CF₂CF₂—O—CF₂—CF₂— is a perfluoroalkylene groupinterrupted by an —O—.

All numerical ranges are inclusive of their endpoints and nonintegralvalues between the endpoints unless otherwise stated (e.g., 1 to 5includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

DETAILED DESCRIPTION

The copolymer according to the present disclosure includes divalentunits represented by formula —[CF₂—CF_(2])—. In some embodiments, thecopolymer according to the present disclosure comprise at least 60 mole% of divalent units represented by formula —[CF₂—CF_(2])—, based on thetotal moles of divalent units. In some embodiments, the copolymercomprises at least 65, 70, 75, 80, or 90 mole % of divalent unitsrepresented by formula —[CF₂—CF_(2])—, based on the total moles ofdivalent units. Divalent units represented by formula —[CF₂—CF₂]— areincorporated into the copolymer by copolymerizing components includingtetrafluoroethylene (TFE). In some embodiments, the components to bepolymerized include at least 60, 65, 70, 75, 80, or 90 mole % TFE, basedon the total moles of components to be polymerized.

The copolymer according to the present disclosure includes divalentunits independently represented by formula:

In this formula, a is 0 or 1, b is a number from 2 to 8, c is a numberfrom 0 to 2, and e is a number from 1 to 8. In some embodiments, b is anumber from 2 to 6 or 2 to 4. In some embodiments, b is 2. In someembodiments, e is a number from 1 to 6 or 2 to 4. In some embodiments, eis 2. In some embodiments, e is 4. In some embodiments, c is 0 or 1. Insome embodiments, c is 0. In some embodiments, c is 0, and e is 2 or 4.In some embodiments, c is 0, and e is 3 to 8, 3 to 6, 3 to 4, or 4. Insome embodiments, at least one of c is 1 or 2 ore is 3 to 8, 3 to 6, 3to 4, or 4. In some embodiments, when a and c are 0, then e is 3 to 8, 3to 6, 3 to 4, or 4. In some embodiments, b is 3, c is 1, and e is 2. Insome embodiments, b is 2 or 3, c is 1, and e is 2 or 4. In someembodiments, a, b, c, and e may be selected to provide greater than 2,at least 3, or at least 4 carbon atoms. C_(e)F_(2e) may be linear orbranched. In some embodiments, C_(e)F_(2e) can be written as (CF₂)_(e),which refers to a linear perfluoroalkylene group. When c is 2, the b inthe two C_(b)F_(2b) groups may be independently selected. However,within a C_(b)F_(2b) group, a person skilled in the art would understandthat b is not independently selected. Also in this formula and in any—SO₂X end groups that may be present, X is independently —F, —NZH,—NZSO₂(CF₂)₁₋₆SO₂X′, —NZ[SO₂(CF₂)_(d)SO₂NZ]₁₋₁₀SO₂(CF₂)_(d)SO₂X′ (inwhich each d is independently 1 to 6, 1 to 4, or 2 to 4), or —OZ. Insome embodiments, X is independently —F, —NZH, or —OZ. In someembodiments, X is —NZH or —OZ. In some embodiments, X is —OZ. In someembodiments, X is independently —NZH, —NZSO₂(CF₂)₁₋₆SO₂X′, or—NZ[SO₂(CF₂)_(d)SO₂NZ]₁₋₁₀SO₂(CF₂)_(d)SO₂X′. X′ is independently —NZH or—OZ (in some embodiments, —OZ). In any of these embodiments, each Z isindependently a hydrogen, alkyl having up to 4, 3, 2, or 1 carbon atoms,an alkali metal cation, or a quaternary ammonium cation. The quaternaryammonium cation can be substituted with any combination of hydrogen andalkyl groups, in some embodiments, alkyl groups independently havingfrom one to four carbon atoms. In some embodiments, Z is an alkali-metalcation. In some embodiments, Z is a sodium or lithium cation. In someembodiments, Z is a sodium cation. Copolymers having divalent unitsrepresented by this formula can be prepared by copolymerizing componentsincluding at least one polyfluoroallyloxy or polyfluorovinyloxy compoundrepresented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″, in which a, b,c, and e are as defined above in any of their embodiments, and each X″is independently —F, —NZH, or —OZ. Suitable polyfluoroallyloxy andpolyfluorovinyloxy compounds of this formula includeCF₂═CFCF₂—O—CF₂—SO₂X″, CF₂═CFCF₂—O—CF₂CF₂—SO₂X″,CF₂═CFCF₂—O—CF₂CF₂CF₂—SO₂X^(″, CF) ₂═CFCF₂—O—CF₂CF₂CF₂CF₂—SO₂X″,CF₂═CFCF₂—O—CF₂CF(CF₃)—O—(CF₂)_(e)—SO₂X″, CF₂═CF—O—CF₂—SO₂X″,CF₂═CF—O—CF₂CF₂—SO₂X″, CF₂═CF—O—CF₂CF₂CF₂—SO₂X″,CF₂═CF—O—CF₂CF₂CF₂CF₂—SO₂X″, and CF₂═CF—O—CF₂═CF(CF₃)—O—(CF₂)_(e)—SO₂X″.In some embodiments, the compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ isCF₂═CFCF₂—O—CF₂CF₂—SO₂X″, CF₂═CF—O—CF₂CF₂—SO₂X″,CF₂═CFCF₂—O—CF₂CF₂CF₂CF₂—SO₂X″, or CF₂═CF—O—CF₂CF₂CF₂CF₂—SO2X″. In someembodiments, the compound represented by formulaCF₂CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ isCF₂CFCF₂—O—CF₂CF₂—SO₂X″, CF₂═CFCF₂—O—CF₂CF₂CF₂CF₂—SO₂X″, orCF₂=CF—O—CF₂CF₂CF₂CF₂—SO₂X″. In some embodiments, the compoundrepresented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ isCF₂CFCF₂—O—CF₂CF₂—SO₂X″ or CF₂═CFCF2-O—CF₂CF₂CF₂CF₂—SO₂X″.

Compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ can be made byknown methods. For example, acid fluorides represented by formulaFSO₂(CF₂)_(e−1)—C(O)F or FSO₂(CF₂)_(c)—(OC_(b)F_(2b))_(c−1)—C(O)F can bereacted with perfluoroallyl chloride, perfluoroallyl bromide, orperfluoroallyl fluorosulfate in the presence of potassium fluoride asdescribed in U.S. Pat. No. 4,273,729

(Krespan) to make compounds of formulaCF₂═CFCF₂—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂F. Compounds of formulaCF₂═CFCF₂—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂F can be hydrolyzed witha base (e.g., alkali metal hydroxide or ammonium hydroxide) to provide acompound represented by formulaCF₂═CFCF₂—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′.

In some embodiments of the copolymer according to the presentdisclosure, at least some of the fluorinated divalent units are derivedfrom at least one short-chain SO₂X″-containing vinyl ether monomer.Likewise, short-chain SO₂X″-containing vinyl ether monomers may beuseful components to be polymerized in the methods according to thepresent disclosure. Short-chain SO₂X″-containing vinyl ether monomersrepresented by formula CF₂═CF—O—(CF₂)₂—SO₂X″ (e.g., those represented byformula [CF₂═CF—O—(CF₂)₂—SO₃]M, where M is an alkali metal, andCF₂═CF—O—(CF₂)₂—SO₂NZH) can be made by known methods. Conveniently, acompound of formula [CF₂═CF—O—(CF₂)₂—SO₃]M can be prepared in threesteps from the known compound represented by formulaFC(O)—CF(CF₃)—O—(CF₂)₂—SO₂F. As reported in Gronwald, O., et al;“Synthesis of difluoroethyl perfluorosulfonate monomer and itsapplication”; J. Fluorine Chem., 2008, 129, 535-540, the acid fluoridecan be combined with a methanol solution of sodium hydroxide to form thedisodium salt, which can be dried and heated in dry diglyme to effectthe carboxylation. FC(O)—CF(CF₃)—O—(CF₂)₂—SO₂F can be prepared byring-opening and derivatization of tetrafluoroethane-β-sultone asdescribed in U.S. Pat. No. 4,962,292 (Marraccini et al.). Compoundsrepresented by formula CF₂═CF—O—(CF₂)_(a)—SO₂X″ can also be prepared byhydrolyzing the products from the elimination of halogen from a compoundof formula CF₂Cl—CFC—O—(CF₂)₂—SO₂F described in U.S. Pat. No. 6,388,139(Resnick) and or hydrolyzing the products of decarboxylation ofFSO₂—(CF₂)₃₋₄—O—CF(CF₃)—COO⁻)_(p)M⁺P described in U.S. Pat. No.6,624,328 (Guerra). Compounds of formula CF₂═CF—O—(CF₂)₂—SO₂NH₂ can beprepared, for example, by reaction of a cyclic sulfone with oneequivalent of LHMDS as described by Uematsu, N., et al. “Synthesis ofnovel perfluorosulfonamide monomers and their application”; J. FluorineChem., 2006, 127, 1087-1095.

In some embodiments of the copolymer according to the presentdisclosure, the copolymer includes divalent units independentlyrepresented by formula

In this formula, m′ is 0 or 1, and Rf₁ is a branched perfluoroalkylgroup having from 3 to 8 carbon atoms. However, when m′ is 1, Rf₁ can bea branched perfluoroalkyl group having from 3 to 8 carbon atoms or alinear perfluoroalkyl group having 5 to 8 carbon atoms. In someembodiments, Rf₁ is a branched perfluoroalkyl group having from 3 to 6or 3 to 4 carbon atoms. An example of a useful perfluoroalkyl vinylether (PAVE) from which these divalent units are derived isperfluoroisopropyl vinyl ether (CF₂═CFOCF(CF₃)₂), also called iso-PPVE.

In some embodiments of the copolymer according to the presentdisclosure, the copolymer includes divalent units independentlyrepresented by formula

In this formula Rf is a linear or branched perfluoroalkyl group havingfrom 1 to 8 carbon atoms and optionally interrupted by one or more —O—groups, z is 1 or 2, each n is independently from 1 to 4, and m is 0or 1. In some embodiments, n is 1, 3, or 4, or from 1 to 3, or from 2 to3, or from 2 to 4. One n can be 2, for example, when z is 2. In thesecases, one n is 2, and the other is 1, 3, or 4. When a is 1 in any ofthe formulas described above, for example, n may also be 2. In someembodiments, n is 1 or 3. In some embodiments, n is 1. In someembodiments, n is not 3. When z is 2, the n in the two C_(n)F_(2n)groups may be independently selected. However, within a C_(n)F_(2n)group, a person skilled in the art would understand that n is notindependently selected. C_(n)F_(2n), may be linear or branched. In someembodiments, C_(n)F_(2n) is branched, for example, CF₂—CF(CF₃)—. In someembodiments, C_(n)F_(2n) can be written as (CF₂)_(n), which refers to alinear perfluoroalkylene group. In these cases, the divalent units ofthis formula are represented by formula

In some embodiments, C_(n)F_(2n) is CF₂—CF₂—CF₂—. In some embodiments,(OC_(n)F_(2n))_(z) is represented by —O—(CF₂)₁₋₄[O(CF₂)₁₋₄]₀₋₁. In someembodiments, Rf is a linear or branched perfluoroalkyl group having from1 to 8 (or 1 to 6) carbon atoms that is optionally interrupted by up to4, 3, or 2 —O— groups. In some embodiments, Rf is a perfluoroalkyl grouphaving from 1 to 4 carbon atoms optionally interrupted by one —O— group.

Divalent units represented by formulas

in which m is 0, typically arise from perfluoroalkoxyalkyl vinyl ethers.Suitable perfluoroalkoxyalkyl vinyl ethers (PAOVE) include thoserepresented by formula CF₂═CF[O(CF₂)_(n)]_(z)ORf andCF₂═CF(OC_(n)F_(2n))_(z)ORf, in which n, z, and Rf are as defined abovein any of their embodiments. Examples of suitable perfluoroalkoxyalkylvinyl ethers include CF₂═CFOCF₂OCF₃, CF₂═CFOCF₂OCF₂CF₃,CF₂═CFOCF₂CF₂OCF₃, CF₂═CFOCF₂CF₂CF₂OCF₃, CF₂═CFOCF₂CF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₃, CF₂═CFOCF₂CF₂CF₂OCF₂CF₃,CF₂═CFOCF₂CF₂CF₂CF₂OCF₂CF₃, CF₂═CFOCF₂CF₂OCF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₂OCF₃, CF₂═CFOCF₂CF₂OCF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₂CF₂CF₂OCF₃, CF₂═CFOCF₂CF₂OCF₂CF₂CF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂(OCF₂)₃OCF₃, CF_(2═)CFOCF₂CF₂(OCF₂)₄OCF₃,CF₂═CFOCF₂CF₂OCF₂OCF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₂CF₃CF₂═CFOCF₂CF₂OCF₂CF₂OCF₂CF₂CF₃,CF₂═CFOCF₂CF(CF₃)—O—C₃F₇ (PPVE-2), CF₂═CF(OCF₂CF(CF₃))₂—O—C₃F₇ (PPVE-3),and CF₂═CF(OCF₂CF(CF₃))₃—O—C₃F₇ (PPVE-4). In some embodiments, theperfluoroalkoxyalkyl vinyl ether is selected from CF₂═CFOCF₂OCF₃,CF₂═CFOCF₂OCF₂CF₃, CF₂═CFOCF₂CF₂OCF₃, CF₂═CFOCF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂CF₂CF₂OCF₃, CF₂═CFOCF₂CF₂CF₂OCF₂CF₃,CF₂═CFOCF₂CF₂CF₂CF₂OCF₂CF₃, CF_(2═)CFOCF₂CF₂OCF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₂CF₂OCF₃, CF₂═CFOCF₂CF₂OCF₂CF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₂CF₂CF₂CF₂OCF₃, CF₂═CFOCF₂CF₂(OCF₂)₃OCF₃,CF₂═CFOCF₂CF₂(0CF₂)₄OCF₃, CF₂═CFOCF₂CF₂OCF₂OCF₂OCF₃, and combinationsthereof. Many of these perfluoroalkoxyalkyl vinyl ethers can be preparedaccording to the methods described in U.S. Pat. No. 6,255,536 (Worm etal.) and U.S. Pat. No. 6,294,627 (Worm et al.). In some embodiments, thePAOVE is other than perfluoro-3-methoxy-n-propyl vinyl ether.

The divalent units represented by formula

in which m is 1, are typically derived from at least oneperfluoroalkoxyalkyl allyl ether. Suitable perfluoroalkoxyalkyl allylethers include those represented by formulaCF₂═CFCF₂(OC_(a)F_(2a))_(z)ORf, in which n, z, and Rf are as definedabove in any of their embodiments. Examples of suitableperfluoroalkoxyalkyl allyl ethers include CF₂═CFCF₂OCF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂OCF₃, CF₂═CFCF₂OCF₂OCF₂CF₃,CF₂═CFCF₂OCF₂CF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₃,CF₂═CFCF₂OCF₂CF₂CF₂OCF₂CF₃, CF₂═CFCF₂OCF₂CF₂CF₂CF₂OCF₂CF₃,CF₂═CFCF₂OCF₂CF₂OCF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂(OCF₂)₃OCF₃,CF₂═CFCF₂OCF₂CF₂(OCF₂)₄OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂OCF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂OCF₂CF₂CF₃,CF₂═CFCF₂OCF₂CF(CF₃)—O—C₃F₇, and CF₂═CFCF₂(OCF₂CF(CF₃))₂—O—C₃F₇. In someembodiments, the perfluoroalkoxyalkyl allyl ether is selected fromCF₂═CFCF₂OCF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂OCF₃,CF₂═CFCF₂OCF₂OCF₂CF₃, CF₂═CFCF₂OCF₂CF₂CF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₃, CF₂═CFCF₂OCF₂CF₂CF₂OCF₂CF₃,CF₂═CFCF₂OCF₂CF₂CF₂CF₂OCF₂CF₃, CF₂═CFCF₂OCF₂CF₂OCF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂CF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂(OCF₂)₃OCF₃, CF₂═CFCF₂OCF₂CF₂(OCF₂)₄OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂OCF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂OCF₂CF₂CF₃, and combinations thereof.

Many of these perfluoroalkoxyalkyl allyl ethers can be prepared, forexample, according to the methods described in U.S. Pat. No. 4,349,650(Krespan). Perfluoroalkoxyalkyl allyl ethers can also be prepared bycombining first components comprising at least one of CF₂═CF—CF₂—OSO₂Clor CF₂═CF—CF₂—OSO₂CF₃, a polyfluorinated compound comprising at leastone ketone or carboxylic acid halide or combination thereof, andfluoride ion. Polyfluorinated compounds comprising at least one ketoneor carboxylic acid halide or combination thereof and fluoride ions canbe any of those described, for example, in U.S. Pat. No. 4,349,650(Krespan).

CF₂═CF—CF₂—OSO₂Cl can conveniently be prepared by reaction of borontrichloride (BC1₃) and ClSO₃H to provide B(OSO₂Cl)₃ and subsequentlyreacting the B(OSO₂Cl)₃ and hexafluoropropylene (HFP). The reaction ofBCl₃ and ClSO₃H can be carried out, for example, by dropwise addition ofneat ClSO₃H to gaseous BCl₃ at below 50° C. or, in the case of condensedBCl₃ at sub-ambient temperature. The reaction can be carried out at atemperature of least −20° C., −10° C., 0° C., 10° C., or 20° C. and upto 30° C., 40° C., or 50° C. The addition of ClSO₃H to BCl₃ can becarried out at a rate, for example, to maintain the temperature of themixture at 10° C. or below. B(OSO₂Cl)₃ can be isolated as a white powderafter volatile starting materials are removed under vacuum. B(OSO₂Cl)₃can then be suspended or dissolved in a solvent, and HFP can be added atbelow 50° C., in some embodiments, at sub-ambient temperature. Forexample, the reaction can be carried out at a temperature of least −20°C., −10° C., 0° C., 10° C., or 20° C. and up to 30° C., 40° C., or 50°C. Suitable solvents include halogenated solvents (e.g., methylenechloride or Freon-113). In some embodiments, the solvent is anon-aromatic solvent. CF₂═CF—CF₂—OSO₂Cl can be isolated and optionallypurified using conventional methods.

Combining components comprising M(OSO₂CF₃)₃ and hexafluoropropylene(HFP) to provide CF₂═CF—CF₂—OSO₂CF₃, wherein M is Al or B. Al(OSO₂CF₃)₃is commercially available, for example, from chemical suppliers such asabcr GmbH (Karlsruhe, Germany) and Sigma-Aldrich (St. Louis, Mo.).Reaction of BCl₃ and CF₃SO₃H can be useful to provide B(OSO₂CF₃)₃. Thereaction of BCl₃ and CF₃SO₃H can be carried out, for example, bydropwise addition of neat CF₃SO₃H to gaseous BCl₃ at below 50° C. or, inthe case of condensed BCl₃ at sub-ambient temperature. The reaction canbe carried out at a temperature of least −20° C., −10° C., 0° C., 10°C., or 20° C. and up to 30° C., 40° C., or 50° C. The addition ofCF₃SO₃H to BCl₃ can be carried out at a rate, for example, to maintainthe temperature of the mixture at 10° C. or below. B(OSO₂CF₃)₃ can beisolated as a white powder after volatile starting materials are removedunder vacuum.

B(OSO_(b 2)CF₃)₃ can combined with HFP at a temperature above 0° C. Insome embodiments, the reaction can be carried out at a temperature up to50° C., 40° C., 30° C., 20° C., or 10° C. The reaction can be carriedout at a temperature in a range from above 0° C. to 10° C., in someembodiments, in a range from 2° C. to 10° C., and in some embodiments,in a range from 4° C. to 8° C. The reaction mixture is combined withwater at a temperature below 28° C., in some embodiments, in a rangefrom above 25° C. to 27° C. The reaction product can then be isolatedand optionally purified using conventional methods (e.g., separation ofthe organic fraction, drying over a drying agent, filtering, anddistilling). The product CF₂═CF—CF₂—O—SO₂CF₃ can be isolated in 75%yield, which is an improvement over the yield reported in Petrov, V. A.,J. Fluorine Chem. 1995, 73, 17-19.

The vinyl ethers and allyl ethers described above in any of theirembodiments, may be present in the components to be polymerized in anyuseful amount, in some embodiments, in an amount of up to 20, 15, 10,7.5, or 5 mole percent, of at least 3, 4, 4.5, 5, or 7.5 mole percent,or in a range from 3 to 20, 4 to 20, 4.5 to 20, 5 to 20, 7.5 to 20, or 5to 15 mole percent, based on the total amount of polymerizablecomponents. Accordingly, the copolymer according to the presentdisclosure can include divalent units derived from these vinyl ethersand allyl ethers in any useful amount, in some embodiments, in an amountof up to 20, 15, 10, 7.5, or 5 mole percent, of at least 3, 4, 4.5, 5,or 7.5 mole percent, or in a range from 3 to 20, 4 to 20, 4.5 to 20, 5to 20, 7.5 to 20, or 5 to 15 mole percent, based on the total moles ofdivalent units.

In some embodiments of the copolymer according to the presentdisclosure, the copolymer includes divalent units derived from at leastone fluorinated olefin independently represented by formulaC(R)₂═CF—Rf₂. These fluorinated divalent units are represented byformula [CR₂—CFRf₂]—. In formulas C(R)₂═CF—Rf₂ and [CR₂—CFRf₂]—, Rf₂ isfluorine or a perfluoroalkyl having from 1 to 8, in some embodiments 1to 3, carbon atoms, and each R is independently hydrogen, fluorine, orchlorine. Some examples of fluorinated olefins useful as components ofthe polymerization include, hexafluoropropylene (HFP),trifluorochloroethylene (CTFE), and partially fluorinated olefins (e.g.,vinylidene fluoride (VDF), tetrafluoropropylene (R1234yf),pentafluoropropylene, and trifluoroethylene). In some embodiments, thecopolymer includes at least one of divalent units derived fromchlorotrifluoroethylene or divalent units derived fromhexafluoropropylene. Divalent units represented by formula —[CR₂—CFRf₂]—may be present in the copolymer in any useful amount, in someembodiments, in an amount of up to 10, 7.5, or 5 mole percent, based onthe total moles of divalent units.

In some embodiments of the copolymer and method according to the presentdisclosure, the copolymer is essentially free of VDF units, and thecomponents to be copolymerized are essentially free of VDF. For example,at a pH higher than 8, VDF may undergo dehydrofluorination, and it maybe useful to exclude VDF from the components to be polymerized.“Essentially free of VDF” can mean that VDF is present in the componentsto be polymerized at less than 1 (in some embodiments, less than 0.5,0.1, 0.05, or 0.01) mole percent. “Essentially free of VDF” includesbeing free of VDF.

Copolymers of the present disclosure can comprise divalent unitsindependently represented by formula:

wherein p is 0 or 1, q is 2 to 8, r is 0 to 2, s is 1 to 8, and Z′ is ahydrogen, an alkali-metal cation or a quaternary ammonium cation. Insome embodiments, q is a number from 2 to 6 or 2 to 4. In someembodiments, q is 2. In some embodiments, s is a number from 1 to 6 or 2to 4. In some embodiments, s is 2. In some embodiments, s is 4. In someembodiments, r is 0 or 1. In some embodiments, r is 0. In someembodiments, r is 0, and s is 2 or 4. In some embodiments, q is 3, r is1, and e is 2. C_(s)F_(2s), may be linear or branched. In someembodiments, C_(s)F_(2s) can be written as (CF₂)_(s), which refers to alinear perfluoroalkylene group. When r is 2, the q in the twoC_(q)F_(2q) groups may be independently selected. However, within aC_(q)F_(2q) group, a person skilled in the art would understand that qis not independently selected. Each Z′ is independently a hydrogen, analkali metal cation, or a quaternary ammonium cation. The quaternaryammonium cation can be substituted with any combination of hydrogen andalkyl groups, in some embodiments, alkyl groups independently havingfrom one to four carbon atoms. In some embodiments, Z′ is analkali-metal cation. In some embodiments, Z′ is a sodium or lithiumcation. In some embodiments, Z′ is a sodium cation. Divalent unitsrepresented by formula

may be present in the copolymer in any useful amount, in someembodiments, in an amount of up to 10, 7.5, or 5 mole percent, based onthe total moles of divalent units.

Copolymers of the present disclosure can also include units derived frombisolefins represented by formulaX₂C═CY—(CW₂)_(m)—(O)_(n)—R_(F)—(O)_(o)—(CW₂)_(p)—CY═CX₂. In thisformula, each of X, Y, and W is independently fluoro, hydrogen, alkyl,alkoxy, polyoxyalkyl, perfluoroalkyl, perfluoroalkoxy orperfluoropolyoxyalkyl, m and p are independently an integer from 0 to15, and n, o are independently 0 or 1. In some embodiments, X, Y, and Ware each independently fluoro, CF₃, C₂F₅, C₃F₇, C₄F₉, hydrogen, CH₃,C₂H₅, C₃H₇, C₄H₉. In some embodiments, X, Y, and W are each fluoro(e.g., as in CF₂═CF—O—RF—O—CF═CF₂ and CF₂═CF—CF₂—O—R_(F)—O—CF₂—CF═CF₂).In some embodiments, n and o are 1, and the bisolefins are divinylethers, diallyl ethers, or vinyl-allyl ethers. R_(F) represents linearor branched perfluoroalkylene or perfluoropolyoxyalkylene or arylene,which may be non-fluorinated or fluorinated. In some embodiments, R_(F)is perfluoroalkylene having from 1 to 12, from 2 to 10, or from 3 to 8carbon atoms. The arylene may have from 5 to 14, 5 to 12, or 6 to 10carbon atoms and may be non-substituted or substituted with one or morehalogens other than fluoro, perfluoroalkyl (e.g. —CF₃ and —CF₂CF₃),perfluoroalkoxy (e.g. —O—CF₃, —OCF₂CF₃), perfluoropolyoxyalkyl (e.g.,—OCF₂OCF₃; —CF₂OCF₂OCF₃), fluorinated, perfluorinated, ornon-fluorinated phenyl or phenoxy, which may be substituted with one ormore perfluoroalkyl, perfluoroalkoxy, perfluoropolyoxyalkyl groups, oneor more halogens other than fluoro, or combinations thereof. In someembodiments, R_(F) is phenylene or mono-, di-, tri- ortetrafluoro-phenylene, with the ether groups linked in the ortho, paraor meta position. In some embodiments, R_(F) is CF₂; (CF₂)_(q) wherein qis 2, 3, 4, 5, 6, 7 or 8; CF₂—O—CF₂; CF₂—O—CF₂—CF₂; CF(CF₃)CF₂;(CF₂)₂—O—CF(CF₃)—CF₂; CF(CF₃)—CF₂—O—CF(CF₃)CF₂; or(CF₂)₂—O—CF(CF₃)—CF₂—O—CF(CF₃)—CF₂—O—CF₂. The bisolefins can introducelong chain branches as described in U.S. Pat. Appl. Pub. No.2010/0311906 (Lavallée et al.). The bisolefins, described above in anyof their embodiments, may be present in the components to be polymerizedin any useful amount, in some embodiments, in an amount of up to 2, 1,or 0.5 mole percent and in an amount of at least 0.1 mole percent, basedon the total amount of polymerizable components.

Copolymers of the present disclosure can also include units derived fromnon-fluorinated monomers. Examples of suitable non-fluorinated monomersinclude ethylene, propylene, isobutylene, ethyl vinyl ether, vinylbenzoate, ethyl allyl ether, cyclohexyl allyl ether, norbomadiene,crotonic acid, an alkyl crotonate, acrylic acid, an alkyl acrylate,methacrylic acid, an alkyl methacrylate, and hydroxybutyl vinyl ether.Any combination of these non-fluorinated monomers may be useful. In someembodiments, the components to be polymerized further include acrylicacid or methacrylic acid, and the copolymer of the present disclosureincludes units derived from acrylic acid or methacrylic acid.

Typically, the copolymer of the present disclosure does not includecyclic structures comprising fluorinated carbon atoms and oxygen atomsin the main chain (that is, divalent units comprising such cyclicstructures).

In some embodiments, the copolymer according to the present disclosurecan be made from the sulfonyl fluoride compounds, where X″ in any of theaforementioned compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ is F, accordingto the methods described below, for example. In these embodiments, the—SO₂F groups may be hydrolyzed or treated with ammonia usingconventional methods to provide —SO₃Z or —SO₂NZH groups. Hydrolysis of acopolymer having —SO₂F groups with an alkaline hydroxide (e.g. LiOH,NaOH, or KOH) solution provides —SO₃Z groups, which may be subsequentlyacidified to SO₃H groups. Treatment of a copolymer having —SO₂F groupswith water and steam can form SO₃H groups. Thus, copolymers of thepresent disclosure having —SO₂F groups (that is, in which X is F) areuseful intermediates for making other copolymers of the presentdisclosure.

In some embodiments, the method according to the present disclosureincludes copolymerizing components including at least one compoundrepresented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′, in which b, c,and e are as defined above in any of their embodiments. In this formula,X′ is —NZ′H or —OZ′, wherein each Z′ is independently a hydrogen, analkali metal cation, or a quaternary ammonium cation. The quaternaryammonium cation can be substituted with any combination of hydrogen andalkyl groups, in some embodiments, alkyl groups independently havingfrom one to four carbon atoms. In some embodiments, Z′ is analkali-metal cation. In some embodiments, Z′ is a sodium or lithiumcation. In some embodiments, Z′ is a sodium cation. In some embodiments,the compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′ isCF₂═CFCF₂—O—CF₂CF₂—SO₃Na.

The copolymer according to the present disclosure can have an —SO₂Xequivalent weight of up to 2000, 1900, 1800, 1750, 1500, 1400, 1300,1200, 1100, 1000, 900, 800, 750, 700, or 600. In some embodiments, thecopolymer has an —SO₂X equivalent weight of at least 300, 400, 500, 600,700, 800, 900, 950, or 1000. In some embodiments, the copolymer orionomer has an —SO₂X equivalent weight in a range from 800 to 2000, 950to 2000, or 1000 to 2000. In some embodiments, the copolymer has an—SO₃Z equivalent weight in a range from 300 to 1400, 300 to 1300, 300 to1200, 400 to 1200, or 400 to 1000. In general, the S02X equivalentweight of the copolymer refers to the weight of the copolymer containingone mole of —SO₂X groups, wherein X is as defined above in any of itsembodiments. In some embodiments, the —SO₂X equivalent weight of thecopolymer refers to the weight of the copolymer that will neutralize oneequivalent of base. In some embodiments, the —SO₂X equivalent weight ofthe copolymer refers to the weight of the copolymer containing one moleof sulfonate groups (i.e., —SO₃ ⁻). Decreasing the —SO₂X equivalentweight of the copolymer or ionomer tends to increase proton conductivityin the copolymer or ionomer but tends to decrease its crystallinity,which may compromise the mechanical properties of the copolymer. Thus,the —SO₂X equivalent weight may be selected based on a balance of therequirements for the electrical and mechanical properties of thecopolymer or ionomer. In some embodiments, the —SO₂X equivalent weightof the copolymer refers to the weight of the copolymer containing onemole of sulfonamide groups (i.e., —SO₂NH). Sulfonimide groups (e.g.,when X is —NZSO₂(CF₂)₁₋₆SO₂X′ and—NZ[SO₂(CF₂)_(a)SO₂NZ]₁₋₁₀SO₂(CF₂)_(a)SO₂X′) also function as acidgroups that can neutralize base as described in further detail below.The effect equivalent weight of copolymers including these groups can bemuch lower than 1000. Equivalent weight can be calculated from the molarratio of monomer units in the copolymer using, for example, the equationshown in the Examples, below.

The copolymer according to the present disclosure can have up to 30 molepercent of divalent units independently represented by formula

based on the total amount of the divalent units. In some embodiments,the copolymer comprises up to 25 or 20 mole percent of these divalentunits, based on the total amount of these divalent units. The componentsthat are copolymerized in the methods described herein can comprise upto 30 mole percent of at least one compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X orCF₂CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′, in any of theirembodiments described above, based on the total amount of components. Insome embodiments, the components comprise up to 25 or 20 mole percent ofa compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ orCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′, based on thetotal amount of components.

The molecular weights of copolymers according to the present disclosurecan be characterized by the melt viscosity or the melt flow index (MFI,e.g., 265° C./5 kg) of a variation of the copolymer in which X is F. Insome embodiments, the copolymer of the present disclosure has an MFI ofup to 80 grams per 10 minutes, 70 grams per 10 minutes, 60 grams per 10minutes, 50 grams per 10 minutes, 40 grams per 10 minutes, 30 grams per10 minutes, or 20 grams per 10 minutes. In some embodiments, thecopolymer according to the present disclosure has an MFI of up to 15grams per 10 minutes or up to 12 grams per 10 minutes. When the MFI isup to 80, 70, 60, 50, 40, 30, 20, 15, or 12 grams per 10 minutes, goodmechanical properties are achieved. The MFI of a copolymer can beaffected by adjusting the amount of the initiator and/or chain-transferagent used during polymerization, both of which affect the molecularweight and molecular-weight distribution of the copolymer. MFI can alsobe controlled by the rate of addition of initiator to thepolymerization. Variations in the monomer composition can also affectthe MFI. For the purposes of the present disclosure, MFI is measuredaccording to the test method described in the Examples, below. It shouldbe noted that an MFI of about 20 grams per 10 minutes measured at 270°C./2.16 kg will give an MFI of 43 grams per 10 minutes measured at 265°C./5 kg. In general, when an MFI is measured at 265° C./5 kg, a value ofmore than twice than an MFI measured at 270° C./2.16 kg is obtained.

In some embodiments, copolymers of the present disclosure are ionomers(e.g., when X is other than F). Ionomers typically exhibit a thermaltransition between a state in which the ionic clusters are closelyassociated and a state in which the interactions between those clustershave been weakened. This transition is described as an alpha transition,and the transition temperature is T(α). Ionomers with higher T(α)typically have greater mechanical integrity at elevated temperaturesthan corresponding materials with lower T(α). As a result, to obtainhigh service temperatures for an ionomer, a relatively high T(α) can bedesirable for ionomers. In some embodiments, the α-dispersiontemperature T(α) of copolymers of the present disclosure is at least 95°C., 100° C., 105° C., 110° C., or 115° C. However, we have found thatdecreasing the T(α) can increase oxygen permeability and that selectinga T(α) to obtain a balance of mechanical integrity and oxygenpermeability can be useful. In some embodiments, the a-dispersiontemperature [T(α)] of copolymer of the present disclosure is up to 110°C., 105° C., or 100° C., or less than 100° C., in some embodiments, upto 99.5° C. or 99° C. In some embodiments, the α-dispersion temperature[T(α)] of copolymer of the present disclosure is at least roomtemperature (e.g., 25° C.), in some embodiments, at least 60° C., 65°C., 70° C., 75° C., 80° C., 85° C., 90° C., or 95° C. In someembodiments, the α-dispersion temperature [T(α)] of copolymer of thepresent disclosure is in a range from 60° C. to 100° C., 70° C. to 100°C., 80° C. to 100° C., 90° C. to 100° C., or 95° C. to 100° C. In someembodiments, the α-dispersion temperature [T(α)] of copolymer of thepresent disclosure is in a range from 60° C. to 99.5° C., 70° C. to99.5° C., 80° C. to 99.5° C., 90° C. to 99.5° C., or 95° C. to 99.5° C.In some embodiments, the α-dispersion temperature [T(α)] of copolymer ofthe present disclosure is in a range from 60° C. to 70° C. to 99° C.,80° C. to 99° C., 90° C. to 99° C. or 95° C. to 99° C. In the copolymersof the present disclosure, various factors can affect the [T(α)]. Forexample, when a, b, c, and e are selected to provide greater than 2, atleast 3, or at least 4 carbon atoms in the side chain of thesulfonyl-substituted divalent units a T(α) up to 100° C. (e.g., in arange from 80° C. to 100° C., 90° C. to 100° C., or 95° C. to 100° C.)may be achieved. Also, when m, m′, n, z, Rf, and Rf₁ are selected toprovide greater than 2, at least 3, or at least 4 carbon atoms and/or atleast one or 2 oxygen atoms in the side chain of the divalent unitsrepresented by formula

a T(α) up to 100° C. (e.g., in a range from 80° C. to 100° C., 90° C. to100° C., or 95° C. to 100° C.) may be achieved. Including more than 3,4, 4.5, 5, or 7.5 mol percent of these divalent units can be useful forachieving a T(α) in these ranges. Also, the cation present in theionomer affects the T(α). Thus, T(α) in the copolymer of the presentdisclosure can be changed, for example, by ion exchange.

Dynamic mechanical analysis (DMA) is a useful tool for measuring T(α),as polymer physical property changes accompany this transition. The DMAsample cell may be set up in torsion, compression, or tension. For thepurposes of this disclosure, T(α) is measured by the method described inthe Examples, below. Since the T(α) changes with different cations, forthe purposes of this disclosure, the T(α) is understood to be the T(α)when Z is hydrogen.

The glass transition temperature (Tg) is typically defined as thetemperature at which an amorphous polymer or amorphous region within apolymer transitions from a glassy material (below Tg) to a rubbery one(above Tg). Gas diffusion rates are correlated to free volume in apolymer [see, for example, Diffusion in Polymers, Marcel Dekker (NewYork), 1996, edited by P. Neogi]. The free volume increases withtemperature, particularly so above the Tg of the polymer. The moleculartransport of a gas is enhanced the more the temperature of operationexceeds the Tg of the polymer. As a result, polymers having a relativelylow Tg can be desirable for applications in which gas diffusion isrequired. In some embodiments, in the copolymers of the presentdisclosure, a, b, c, and e may be selected to provide greater than 2, atleast 3, or at least 4 carbon atoms in the side chain of thesulfonyl-substituted divalent units to achieve a lower Tg. In someembodiments, the copolymer in which X is F has a Tg less than 30° C.,less than room temperature, or up to 25° C., 20° C., 15° C., or 10° C.Since multiple bulk physical properties of the polymer are different inthe glassy state relative to the rubbery state, a variety of methods canbe used to measure the Tg. Differential scanning calorimetry (DSC) anddilatometry detect changes in the heat capacity and thermal expansion ofthe polymer in the two states, while methods such as thermal mechanicalanalysis (TMA) and dynamic mechanic analysis (DMA) detect differences inthe physical properties in the two states. For the purposes of thisdisclosure, Tg is measured by the method described in the Examples,below.

In some embodiments, the copolymer of the present disclosure has atleast one of a relative high T(α) (e.g., at least 100° C., 105° C., 110°C., 115° C., 120° C., or 125° C.) or a relative low Tg (e.g., up to 25°C., 20° C., 15° C., or 10° C.). In some embodiments, the copolymer ofthe present disclosure has at least one of a relative low T(α) (e.g., upto 110° C., 105° C., or 100° C.) or a relative low Tg (e.g., up to 25°C., 20° C., 15° C., or 10° C.). In some embodiments, the copolymer ofthe present disclosure has both a relative high T(α) (e.g., at least100° C., 105° C., 110° C., 115° C., 120° C., or 125° C.) and a relativelow Tg (e.g., up to 25° C., 20° C., 15° C., or 10° C.). In someembodiments, the copolymer of the present disclosure has both a relativelow T(α) (e.g., up to 110° C., 105° C., or 100° C.) and a relative lowTg (e.g., up to 25° C., 20° C., 15° C., or 10° C.).

High oxygen permeability in the copolymers disclosed herein can beuseful to improve the efficiency of fuel cells, for example. Copolymersof the present disclosure typically have useful oxygen permeabilitiesfor fuel cell applications. Oxygen permeability can be measured bymethods known in the art including the time lag method described in theExamples, below. As shown in a comparison of Example 1 and ComparativeExample A in the Examples below, the addition of the divalent unitrepresented by formula

can quadruple the oxygen permeability of a copolymer in comparison to acomparable copolymer that does not include these units. Comparable canmean similar to the copolymer of the present disclosure in equivalentweight. The addition of the divalent unit represented by formula

in which m, n, z, and Rf are as defined above, unexpectedly can increasethe oxygen permeability of a copolymer by an order of magnitude incomparison to a comparable copolymer that does not include these units.Furthermore, as shown in a comparison of Example 1 and IllustrativeExample 3, the addition of the divalent unit represented by formula

in which m, n, z, and Rf are as defined above, can increase the oxygenpermeability of a copolymer by an unexpectedly greater amount incomparison to a comparable copolymer that includes divalent unitsderived from CF₂═CF—O—(CF₂)₂—CF₃ instead of the divalent unitrepresented by formula

In some embodiments, including embodiments in which a lower equivalentweight is desired, the copolymer may be crosslinked to improve, forexample, its durability. One useful method of crosslinking is e-beamcrosslinking a copolymer that includes chloro, bromo, or iodo groups asdescribed in U.S. Pat. No. 7,265,162 (Yandrasits et al.). Incorporatingchloro, bromo, or iodo groups, in some embodiments, bromo or iodogroups, into the copolymer prepared by the method disclosed herein canbe carried out by including compounds having formula CX₂═CX(Q) in thecomponents to be polymerized. In formula CX₂═CX(Q), each X isindependently H or F, and W is I, Br, or R_(f)-Q, wherein Q is I or Brand RF is a perfluorinated or partially perfluorinated alkylene groupoptionally containing O atoms. Examples of useful monomers of formulaCX₂═CX(Q) include CF₂═CHI, CF₂═CFI, CF₂═CFCF₂I, CF₂═CFCF₂CF₂I,CF₂═CFOCF₂CF₂I, CF₂═CFOCF₂CF₂CF₂I, CF₂═CFOCF₂CF₂CF₂CF₂I,CF₂═CFO(CF₂)₃OCF₂CF₂I, CF₂═CHBr, CF₂═CFBr, CF₂═CFCF₂Br, CF₂═CFOCF₂CF₂Br,CF₂═CFCl, CF₂═CFCF₂Cl, or a mixture thereof. E-beam crosslinking may becarried out on the copolymer, for example, after it is formed into amembrane as described below.

The methods of making the copolymer can be carried out by free-radicalpolymerization. Conveniently, in some embodiments, the methods of makingthe copolymer disclosed herein includes radical aqueous emulsionpolymerization.

In some embodiments of the methods of making the copolymer according tothe present disclosure, a water-soluble initiator (e.g., potassiumpermanganate or a peroxy sulfuric acid salt) can be useful to start thepolymerization process. Salts of peroxy sulfuric acid, such as ammoniumpersulfate or potassium persulfate, can be applied either alone or inthe presence of a reducing agent, such as bisulfites or sulfinates(e.g., fluorinated sulfinates disclosed in U.S. Pat. Nos. 5,285,002 and5,378,782, both to Grootaert) or the sodium salt of hydroxy methanesulfinic acid (sold under the trade designation “RONGALIT”, BASFChemical Company, New Jersey, USA). The choice of initiator and reducingagent, if present, will affect the end groups of the copolymer. Theconcentration range for the initiators and reducing agent can vary from0.001% to 5% by weight based on the aqueous polymerization medium.

In some embodiments of the method of making the copolymer, —SO₂X endgroups are introduced in the copolymers according to the presentdisclosure by generating SO₃ ⁻ radicals during the polymerizationprocess. When salts of peroxy sulfuric acid are used in the presence ofa sulfite or bisulfite salt (e.g., sodium sulfite or potassium sulfite),SO₃ ⁻ radicals are generated during the polymerization process,resulting in —SO₃ ⁻ end groups. It might be useful to add metal ions tocatalyze or accelerate the formation of —SO₃ ⁻ radicals. By altering thestoichiometry of the sulfite or bisulfite salt versus the peroxysulfuric acid salt, one can vary the amount of —SO₂X end groups.

Most of the initiators described above and any emulsifiers that may beused in the polymerization have an optimum pH-range where they show mostefficiency. Also, a pH can be selected for the method according to thepresent disclosure such that the polymerization is carried out with thesalt form of the compound of formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′, wherein X′ isan alkali metal cation or an ammonium cation, and to maintain the saltform of the copolymer. For these reason, buffers may be useful. Buffersinclude phosphate, acetate, or carbonate (e.g., (NH₄)₂CO₃ or NaHCO₃)buffers or any other acid or base, such as ammonia or alkali-metalhydroxides. In some embodiments, the copolymerizing is carried out at apH of at least 8, higher than 8, at least 8.5, or at least 9. Theconcentration range for the initiators and buffers can vary from 0.01%to 5% by weight based on the aqueous polymerization medium. In someembodiments, ammonia is added to the reaction mixture in an amount toadjust the pH to at least 8, higher than 8, at least 8.5, or at least 9.

Typical chain-transfer agents like H₂, lower alkanes, alcohols, ethers,esters, and CH₂Cl₂ may be useful in the preparation of the copolymer andionomer according to the present disclosure. Termination primarily viachain-transfer results in a polydispersity of about 2.5 or less. In someembodiments of the method according to the present disclosure, thepolymerization is carried out without any chain-transfer agents. A lowerpolydispersity can sometimes be achieved in the absence ofchain-transfer agents. Recombination typically leads to a polydispersityof about 1.5 for small conversions.

Useful polymerization temperatures can range from 20° C. to 150° C.Typically, polymerization is carried out in a temperature range from 30°C. to 120° C., 40° C. to 100° C., or 50° C. to 90° C. The polymerizationpressure is usually in the range of 0.4 MPa to 2.5 MPa, 0.6 to 1.8 MPa,0.8 MPa to 1.5 MPa, and in some embodiments is in the range from 1.0 MPato 2.0 MPa. Fluorinated monomers such as HFP can be precharged and fedinto the reactor as described, for example, in Modern Fluoropolymers,ed. John Scheirs, Wiley & Sons, 1997, p. 241. Perfluoroalkoxyalkyl vinylethers represented by formula CF₂═CF(OC_(n),F_(2n))_(z)ORf andperfluoroalkoxyalkyl allyl ethers represented by formulaCF₂═CFCF₂(OC_(n)F_(2n))_(z)ORf, wherein n, z, and Rf are as definedabove in any of their embodiments, are typically liquids and may besprayed into the reactor or added directly, vaporized, or atomized.

Conveniently, in some embodiments of the method of making the copolymeraccording to the present disclosure, the polymerization process may beconducted with no emulsifier (e.g., no fluorinated emulsifier).Surprisingly, we have found that even with the incorporation of liquidperfluoroalkoxyalkyl vinyl or perfluoroalkoxyalkyl allyl ethers orbisolefins in larger amounts, no fluorinated emulsifier is needed toensure proper incorporation of these monomers. It can be useful to feedthe compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ and thenon-functional comonomers (e.g., perfluoroalkoxyalkyl vinyl orperfluoroalkoxyalkyl allyl ethers or bisolefins) as a homogenous mixtureto the polymerization. In some embodiments, it is possible to hydrolyzesome of the CF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂F(e.g., up to 5 ppm) to obtain an “in situ”-emulsifier. Advantageously,this method may be conducted in the absence of any other fluorinatedemulsifiers.

In some embodiments, however, perfluorinated or partially fluorinatedemulsifiers may be useful. Generally these fluorinated emulsifiers arepresent in a range from about 0.02% to about 3% by weight with respectto the polymer. Polymer particles produced with a fluorinated emulsifiertypically have an average diameter, as determined by dynamic lightscattering techniques, in range of about 10 nanometers (nm) to about 500nm, and in some embodiments in range of about 50 nm to about 300 nm.Examples of suitable emulsifiers include perfluorinated and partiallyfluorinated emulsifier having the formula [R_(f)—O-L-COO⁻]_(i)X^(i+)wherein L represents a linear partially or fully fluorinated alkylenegroup or an aliphatic hydrocarbon group, R_(f) represents a linearpartially or fully fluorinated aliphatic group or a linear partially orfully fluorinated aliphatic group interrupted with one or more oxygenatoms, X^(i+) represents a cation having the valence i and i is 1, 2 or3. (See, e.g., U.S. Pat. No. 7,671,112 to Hintzer et al.). Additionalexamples of suitable emulsifiers also include perfluorinated polyetheremulsifiers having the formula CF₃—(OCF₂)_(x)—O—CF₂—X′, wherein x has avalue of 1 to 6 and X′ represents a carboxylic acid group or saltthereof, and the formula CF₃—O—(CF₂)₃—(OCF(CF₃)—CF₂)_(y)—O—L-Y′ whereiny has a value of 0, 1, 2 or 3, L represents a divalent linking groupselected from —CF(CF₃)—, —CF₂—, and —CF₂CF₂—, and Y′ represents acarboxylic acid group or salt thereof (See, e.g., U.S. Pat. Publ. No.2007/0015865 to Hintzer et al.). Other suitable emulsifiers includeperfluorinated polyether emulsifiers having the formulaR_(f)—O(CF₂CF₂O)CF₂COOA wherein R_(f) is C_(b)F_((2b+i)); where b is 1to 4, A is a hydrogen atom, an alkali metal or NH₄, and xis an integerof from 1 to 3. (See, e.g., U.S. Pat. Publ. No. 2006/0199898 to Funakiet al.). Suitable emulsifiers also include perfluorinated emulsifiershaving the formula F(CF₂)_(b)O(CF₂CF₂O)_(x)CF₂COOA wherein A is ahydrogen atom, an alkali metal or NH₄, b is an integer of from 3 to 10,and x is 0 or an integer of from 1 to 3. (See, e.g., U.S. Pat. Publ. No.2007/0117915 to Funaki et al.). Further suitable emulsifiers includefluorinated polyether emulsifiers as described in U.S. Pat. No.6,429,258 to Morgan et al. and perfluorinated or partially fluorinatedalkoxy acids and salts thereof wherein the perfluoroalkyl component ofthe perfluoroalkoxy has 4 to 12 carbon atoms, or 7 to 12 carbon atoms.(See, e.g., U.S. Pat. No. 4,621,116 to Morgan). Suitable emulsifiersalso include partially fluorinated polyether emulsifiers having theformula [R_(f)—(O)_(t)—CHF—(CF₂)_(x)—COO—]_(i)X^(i+) wherein R_(f)represents a partially or fully fluorinated aliphatic group optionallyinterrupted with one or more oxygen atoms, t is 0 or 1 and xis 0 or 1,X^(i+) represents a cation having a valence i and i is 1, 2 or 3. (See,e.g., U.S. Pat. Publ. No. 2007/0142541 to Hintzer et al.). Furthersuitable emulsifiers include perfluorinated or partially fluorinatedether-containing emulsifiers as described in U.S. Pat. Publ. Nos.2006/0223924, 2007/0060699, and 2007/0142513 each to Tsuda et al. and2006/0281946 to Morita et al. Fluoroalkyl, for example, perfluoroalkylcarboxylic acids and salts thereof having 6-20 carbon atoms, such asammonium perfluorooctanoate (APFO) and ammonium perfluorononanoate (see,e.g., U.S. Pat. No. 2,559,752 to Berry) may also be useful.Conveniently, in some embodiments, the method of making the copolymeraccording to the present disclosure may be conducted in the absence ofany of these emulsifiers or any combination thereof.

If fluorinated emulsifiers are used, the emulsifiers can be removed orrecycled from the fluoropolymer latex, if desired, as described in U.S.Pat. No. 5,442,097 to Obermeier et al., U.S. Pat. No. 6,613,941 to Felixet al., U.S. Pat. No. 6,794,550 to Hintzer et al., U.S. Pat. No.6,706,193 to Burkard et al., and U.S. Pat. No. 7,018,541 to Hintzer etal.

In some embodiments, the obtained copolymer latices are purified by atleast one of anion- or cation-exchange processes to remove functionalcomonomers, anions, and/or cations before coagulation or spray drying(described below). As used herein, the term “purify” refers to at leastpartially removing impurities, regardless of whether the removal iscomplete. Anionic species that may constitute impurities include, forexample, fluoride, anionic residues from surfactants and emulsifiers(e.g., perfluorooctanoate), and residual compounds represented byformula CF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′. Itshould be noted, however, that it may be desirable to not remove ionicfluoropolymer from the dispersion. Useful anion exchange resinstypically comprise a polymer (typically crosslinked) that has aplurality of cationic groups (e.g., quaternary alkyl ammonium groups)paired with various anions (e.g., halide or hydroxide). Upon contactwith the fluoropolymer dispersion, anionic impurities in the dispersionbecome associated with the anion exchange resin. After the anionexchange step, the resultant anion-exchanged dispersion is separatedfrom the anion exchange resin, for example, by filtration. It wasreported in U.S. Pat. No. 7,304,101 (Hintzer et al.) that the anionichydrolyzed fluoropolymer does not appreciably become immobilized on theanion exchange resin, which would lead to coagulation and/or materialloss. Anionic exchange resins are available commercially from a varietyof sources. If the anion exchange resin is not in the hydroxide form itmay be at least partially or fully converted to the hydroxide salt formbefore use. This is typically done by treating the anion exchange resinwith an aqueous ammonia or sodium hydroxide solution. Typically, betteryields are obtained using gel-type anion-exchange resins than withmacroporous anion exchange resins.

Examples of cationic impurities resulting from the abovementionedpolymerization include one or more of, alkali metal cation(s) (e.g.,Li⁺, Na⁺, K⁺), ammonium, quaternary alkyl ammonium, alkaline earthcations (e.g., Mg²⁺, Ca²⁺), manganese cations (e.g. Mn²⁺), and Group IIImetal cations. Useful cation exchange resins include polymers (typicallycross-linked) that have a plurality of pendant anionic or acidic groupssuch as, for example, polysulfonates or polysulfonic acids,polycarboxylates or polycarboxylic acids. Examples of useful sulfonicacid cation exchange resins include sulfonated styrene-divinylbenzenecopolymers, sulfonated crosslinked styrene polymers,phenol-formaldehyde-sulfonic acid resins, andbenzene-formaldehyde-sulfonic acid resins. Carboxylic acid cationexchange resin is an organic acid, cation exchange resin, such ascarboxylic acid cation exchange resin. Cation exchange resins areavailable commercially from a variety of sources. Cation exchange resinsare commonly supplied commercially in either their acid or their sodiumform. If the cation exchange resin is not in the acid form (i.e.,protonated form) it may be at least partially or fully converted to theacid form in order to avoid the generally undesired introduction ofother cations into the dispersion. This conversion to the acid form maybe accomplished by means well known in the art, for example by treatmentwith any adequately strong acid.

If purification of the fluoropolymer dispersion is carried out usingboth anion and cation exchange processes, the anion exchange resin andcation exchange resin may be used individually or in combination as, forexample, in the case of a mixed resin bed having both anion and cationexchange resins.

To coagulate the obtained copolymer latex, any coagulant which iscommonly used for coagulation of a fluoropolymer latex may be used, andit may, for example, be a water-soluble salt (e.g., calcium chloride,magnesium chloride, aluminum chloride or aluminum nitrate), an acid(e.g., nitric acid, hydrochloric acid or sulfuric acid), or awater-soluble organic liquid (e.g., alcohol or acetone). The amount ofthe coagulant to be added may be in a range of 0.001 to 20 parts bymass, for example, in a range of 0.01 to 10 parts by mass per 100 partsby mass of the latex. Alternatively or additionally, the latex may befrozen for coagulation or mechanically coagulated, for example, with ahomogenizer as described in U.S. Pat. No. 5,463,021 (Beyer et al.).Alternatively or additionally, the latex may be coagulated by addingpolycations. It may also be useful to avoid acids and alkaline earthmetal salts as coagulants to avoid metal contaminants. To avoidcoagulation altogether and any contaminants from coagulants, spraydrying the latex after polymerization and optional ion-exchangepurification may be useful to provide solid copolymer.

A coagulated copolymer can be collected by filtration and washed withwater. The washing water may, for example, be ion-exchanged water, purewater, or ultrapure water. The amount of the washing water may be from 1to 5 times by mass to the copolymer or ionomer, whereby the amount ofthe emulsifier attached to the copolymer can be sufficiently reduced byone washing.

The copolymer produced can have less than 50 ppm metal ion content, insome embodiments, less than 25 ppm, less than 10 ppm, less than 5 ppm,or less than 1 ppm metal ion content. Specifically, metal ions such asalkali metals, alkaline earth metal, heavy metals (e.g., nickel, cobalt,manganese, cadmium, and iron) can be reduced. To achieve a metal ioncontent of less than 50 ppm, 25 ppm, 10 ppm. 5 ppm, or 1 ppm,polymerization can be conducted in the absence of added metal ions. Forexample, potassium persulfate, a common alternative initiator orco-initiator with ammonium persulfate, is not used, and mechanical andfreeze coagulation described above may be used instead of coagulationwith metal salts. It is also possible to use organic initiators asdisclosed in U.S. Pat. No. 5,182,342 (Feiring et al.). To achieve suchlow ion content, ion exchange can be used, as described above, and thewater for polymerization and washing may be deionized.

The metal ion content of the copolymer can be measured by flame atomicabsorption spectrometry after combusting the copolymer and dissolvingthe residue in an acidic aqueous solution. For potassium as the analyte,the lower detection limit is less than 1 ppm.

In some embodiments of the methods of making the copolymer according tothe present disclosure, radical polymerization also can be carried outby suspension polymerization. Suspension polymerization will typicallyproduce particle sizes up to several millimeters.

A method for making the copolymers can include copolymerizing componentsincluding SO₂F-containing vinyl and allyl ethers(e.g.,CF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂F),isolating a solid from the polymer dispersion, hydrolyzing the polymer,optionally purifying the polymer by ion exchange purification, anddrying the resulting polymer. In some embodiments, the method of makingthe copolymer includes copolymerizing components including at least onecompound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′, optionallypurifying the copolymer by ion-exchange purification, and spray dryingthe resulting dispersion. This method can conveniently eliminate thesteps of isolating solid polymer and hydrolyzing, resulting in a moreefficient and cost-effective process.

The components to be polymerized in the methods according to the presentdisclosure can include more than one compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″. When more thanone compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″ is present,each of a, b, c, e, and X″ may be independently selected. In someembodiments, the components include compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₃Z andCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂NZH, wherein eacha, b, c, and e is independently selected. The ratio between SO₃Z andSO₂NZH-containing components may range from 99:1 to 1:99. In some ofthese embodiments, each Z is independently an alkali-metal cation or aquaternary ammonium cation.

In some embodiments of the methods according to the present disclosure,compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X′ are notprepared in situ from compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂F. In someembodiments, the components to be polymerized in the method disclosedherein are substantially free of compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(CF₂)—SO₂F. In this regard,“substantially free of compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO_(2F) may mean thatthe components to be polymerized in the method disclosed herein are freeof compounds represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂F or that suchcompounds are present in an amount of up to 5, 4, 3, 2, 1, 0.5, 0.1,0.05, or 0.01 mole percent, based on the total amount of components.

In other embodiments, a copolymer of the present disclosure can be madeby copolymerizing a compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂F and fluorinatedmonomers as described above in any of their embodiments. In theseembodiments, it is possible to hydrolyze some of theCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—O—(C_(e)F_(2e))—SO₂F (e.g., up to 5ppm) to obtain an “in situ”-emulsifier as described above.

Fluoropolymers obtained by aqueous emulsion polymerization withinorganic initiators (e.g. persulfates, KMnO₄, etc.) typically have ahigh number of unstable carbon-based end groups (e.g. more than 200—COOM or —COF end groups per 10⁶ carbon atoms, wherein M is hydrogen, ametal cation, or NH₂). For fluorinated ionomers useful, for example, inan electrochemical cell, the effect naturally increases as sulfonateequivalent weight decreases. These carbonyl end groups are vulnerable toperoxide radical attacks, which reduce the oxidative stability of thefluorinated ionomers. During operation of a fuel cell, electrolysiscell, or other electrochemical cell, peroxides can be formed. Thisdegrades the fluorinated ionomers, and correspondingly reduces theoperational life of the given electrolyte membrane.

As polymerized, the copolymer according to the present disclosure canhave up to 400 —COOM and —COF end groups per 10⁶ carbon atoms, wherein Mis independently an alkyl group, a hydrogen atom, a metallic cation, ora quaternary ammonium cation. Advantageously, in some embodiments, thecopolymer according to the present disclosure has up to 200 unstable endgroups per 10⁶ carbon atoms. The unstable end groups are —COOM or —COFgroups, wherein M is an alkyl group, a hydrogen atom, a metallic cation,or a quaternary ammonium cation. In some embodiments, the copolymer hasup to 150, 100, 75, 50, 40, 30, 25, 20, 15, or 10 unstable end groupsper 10⁶ carbon atoms. The number of unstable end groups can bedetermined by Fourier-transform infrared spectroscopy using the methoddescribed below. In some embodiments, the copolymer according to thepresent disclosure has up to 50 (in some embodiments, up to 40, 30, 25,20, 15, or 10) unstable end groups per 10⁶ carbon atoms, as polymerized.

Copolymers according to some embodiments of the present disclosure have—SO₂X end groups. As described above, —SO₂X end groups can be introducedin the copolymers according to the present disclosure by generating SO₃⁻ radicals during the polymerization process.

In some embodiments, reducing the number of unstable end groups can beaccomplished by carrying out the polymerization in the method disclosedherein in the presence of a salt or pseudohalogen as described in U.S.Pat. No. 7,214,740 (Lochhaas et al.). Suitable salts can include achloride anion, a bromide anion, an iodide anion, or a cyanide anion anda sodium, potassium, or ammonium cation. The salt used in thefree-radical polymerization may be a homogenous salt or a blend ofdifferent salts. Examples of useful pseudohalogens arenitrile-containing compounds, which provide nitrile end groups.Pseudohalogen nitrile-containing compounds have one or more nitrilegroups and function in the same manner as compounds in which the nitrilegroups are replaced with a halogen. Examples of suitable pseudohalogennitrile-containing compounds include NC—CN, NC—S—S—CN, NCS—CN, Cl—CN,Br—CN, I—CN, NCN═NCN, and combinations thereof. During the free-radicalpolymerization, the reactive atoms/groups of the salts or the nitrilegroups of the pseudohalogens chemically bond to at least one end of thebackbone chain of the fluoropolymer. This provides CF₂Y¹ end groupsinstead of carbonyl end groups, wherein Y¹ is chloro, bromo, iodo, ornitrile. For example, if the free-radical polymerization is performed inthe presence of a KCl salt, at least one of the end groups providedwould be a —CF₂Cl end group. Alternatively, if the free-radicalpolymerization is performed in the presence of a NC—CN pseudohalogen, atleast one of the end groups provided would be a —CF₂CN end group.

Post-fluorination with fluorine gas is also commonly used to cope withunstable end groups and any concomitant degradation. Post-fluorinationof the fluoropolymer can convert —COOH, amide, hydride, —COF, —CF₂Y¹ andother nonperfluorinated end groups or —CF═CF₂ to —CF₃ end groups. Thepost-fluorination may be carried out in any convenient manner. Thepost-fluorination can be conveniently carried out with nitrogen/fluorinegas mixtures in ratios of 75-90:25-10 at temperatures between 20° C. and250° C., in some embodiments in a range of 150° C. to 250° C. or 70° C.to 120° C., and pressures from 10 KPa to 1000 KPa. Reaction times canrange from about four hours to about 16 hours. Under these conditions,most unstable carbon-based end groups are removed, whereas —SO₂X groupsmostly survive and are converted to —SO₂F groups. In some embodiments,post-fluorination is not carried out when non-fluorinated monomersdescribed above are used as monomers in the polymerization or when thecopolymer according to the present disclosure includes divalent unitsindependently represented by formula:

as described above in any of their embodiments.

The groups Y¹ in the end groups —CF₂Y¹, described above, are reactive tofluorine gas, which reduces the time and energy required topost-fluorinate the copolymers in these embodiments. We have also foundthat the presence of alkali-metal cations in the copolymer increases thedecomposition rate of unstable carboxylic end-groups and therefore makesa subsequent post-fluorination step, if needed, easier, faster, andcheaper.

For copolymers in which the —SO₂X groups are —SO₂F groups, the copolymercan be treated with an amine (e.g., ammonia) to provide a sulfonamide(e.g., having —SO₂NH₂ groups). Sulfonamides made in this manner orprepared by using CF₂═CFCF₂—(OC_(b)F_(2b))_(c)—O—(CF₂)_(e)—SO₂NH₂ in thecomponents that are polymerized as described above can be furtherreacted with multi-functional sulfonyl fluoride or sulfonyl chloridecompounds. Examples of useful multi-functional compounds include1,1,2,2-tetrafluoroethyl-1,3-disulfonyl fluoride;1,1,2,2,3,3-hexafluoropropyl-1,3-disulfonyl fluoride;1,1,2,2,3,3,4,4-octafluorobutyl-1,4-disulfonyl fluoride;1,1,2,2,3,3,4,4,5,5-perfluoropentyl-1,5-disulfonyl fluoride;1,1,2,2-tetrafluoroethyl-1,2-disulfonyl chloride;1,1,2,2,3,3-hexafluoropropyl-1,3-disulfonyl chloride;1,1,2,2,3,3,4,4-octafluorobutyl-1,4-disulfonyl chloride; and1,1,2,2,3,3,4,4,5,5-perfluoropentyl-1,5-disulfonyl chloride. Afterhydrolysis of the sulfonyl halide groups, the resulting copolymer, inwhich X is —NZSO₂(CF₂)₁₋₆SO₃Z, can have a higher number of ionic groupsthan the copolymer as polymerized. Thus, the number of ionic groups canbe increased and the equivalent weight decreased without affecting thebackbone structure of the copolymer. Also, using a deficient amountmulti-functional sulfonyl fluoride or sulfonyl chloride compounds canresult in crosslinking of the polymer chains, which may be useful toimprove durability in some cases (e.g., for copolymers having lowequivalent weights). Further details can be found, for example, in U.S.Pat. Appl. Publ. No. 20020160272 (Tanaka et al.). To prevent suchcrosslinking, if desired, copolymers bearing —SO₂NH₂ groups can betreated with compounds represented by formula FSO₂(CF₂)₁₋₆SO₃H, whichcan be made by hydrolyzing any of the multi-functional sulfonylfluorides or sulfonyl chlorides described above with one equivalent ofwater in the presence of base (e.g., N,N-diisopropylethylamine (DIPEA))as described in JP 2011-40363, published Feb. 24, 2011. Copolymersbearing SO₂NH₂ groups can also treated with polysulfonimides representedby formula FSO₂(CF₂)_(a)[SO₂NZSO₂(CF₂)_(a)]₁₋₁₀SO₂F orFSO₂(CF₂)_(a)[SO₂NZSO₂(CF₂)_(a)]₁₋₁₀SO₃H, wherein each a isindependently 1 to 6, 1 to 4, or 2 to 4. To make a polysulfonimide, asulfonyl halide monomer (e.g., any of those described above) and asulfonamide monomer represented by formula H₂NSO₂(CF₂)_(a)SO₂NH₂ aremade to react in the mole ratio of (k+1)/k, in which k represents themoles of sulfonamide monomer and k+1 represents the moles of sulfonylhalide monomer. The reaction may be carried out, for example, in asuitable solvent (e.g., acetonitrile) at 0° C. in the presence of base.The sulfonyl halide monomer and sulfonamide monomer may have the same ordifferent values of a, resulting in the same or different value of a foreach repeating unit. The resulting product (e.g.,FSO₂(CF₂)_(a)[SO₂NZSO₂(CF₂)_(a)]₁₋₁₀SO₂F) may be treated with oneequivalent of water in the presence of base (e.g.,N,N-diisopropylethylamine (DIPEA)) to provide, for example,FSO₂(CF₂)_(a)[SO₂NZSO₂(CF₂)_(a)]₁₋₁₀SO₃H, as described in JP 2011-40363.

In other embodiments, copolymers in which the —SO₂X groups are —SO₂Fgroups can be treated with small molecule sulfonamides such as thoserepresented by formula NH₂SO₂(CF₂)₁₋₆SO₃Z, wherein Z is as defined abovein any of its embodiments, to provide —SO₂NHSO₂(CF₂)₁₋₆SO₃Z groups.Compounds represented by formula NH₂SO₂(CF₂)₁₋₆SO₃Z may be synthesizedby reacting cyclic perfluorodisulfonic acid anhydrides with aminesaccording to the methods described in U.S. Pat. No. 4,423,197 (Behr).This can also provide copolymers with very low equivalent weights.

Some conventional fluoropolymers can be difficult to disperse. Atechnique that can be useful for dispersing a fluoropolymer in a desiredmedium is up-concentration of a dilute dispersion of fluoropolymer. Forexample, U.S. Pat. Appl. Pub. Nos. 2017/0183435 (Inc) reports preparinga fluoropolymer electrolyte solution by heating a solid fluoropolymerelectrolyte in a solution of 50% by weight solution of ethanol in waterin an autoclave at 160° C. with stirring for five hours to achieve afluoropolymer electrolyte solution with a solids concentration of 5% byweight. Concentration under reduced pressure provided a fluoropolymerelectrolyte solution with a solids concentration of 20% by weight.

By contrast, the copolymer disclosed herein can typically be directlydispersed at a concentration of at least 10, 15, 20, or 25 percent byweight in a solution of water and organic solvent without the need forup-concentrating. In some embodiments, the copolymer disclosed hereincan be directly dispersed at a concentration of up to 30, 40, or 50percent by weight in a solution of water and organic solvent without theneed for up-concentrating. A useful method includes combining componentscomprising water, an organic solvent, and at least ten percent by weightof the copolymer of the present disclosure, based on the total weight ofthe components, and mixing the components at ambient temperature andpressure to make a fluoropolymer dispersion. In this method, it shouldbe understood that combining components comprising at least ten percentby weight of the copolymer, based on the total weight of the components,refers to the concentration of the copolymer when the components areinitially combined (e.g., when organic solvent is first added to anaqueous dispersion of the fluoropolymer) before any agitation of thecombined components. In some embodiments of this method, X is OZ, and Zis hydrogen. Examples of suitable organic solvents useful for preparingfluoropolymer dispersions of the copolymer of the present disclosureinclude, lower alcohols (e.g., methanol, ethanol, isopropanol,n-propanol), polyols (e.g., ethylene glycol, propylene glycol,glycerol), ethers (e.g., tetrahydrofuran and dioxane), diglyme,polyglycol ethers, ether acetates, acetonitrile, acetone,dimethylsulfoxide (DMSO), N,N dimethyacetamide (DMA), ethylenecarbonate, propylene carbonate, dimethylcarbonate, diethylcarbonate,N,N-dimethylformamide (DMF), N-methylpyrrolidinone (NMP),dimethylimidazolidinone, butyrolactone, hexamethylphosphoric triamide(HMPT), isobutyl methyl ketone, sulfolane, and combinations thereof. Insome embodiments, the copolymer, water, and organic solvent can beheated at a pressure of up to 0.2 MPa or 0.15 MPa at a temperature of upto 100° C., 90° C., 80° C., 70° C., 60° C., 50° C., or 40° C.Advantageously, the fluoropolymer dispersion may also be made at ambienttemperature and pressure.

The copolymer of the present disclosure may be useful, for example, inthe manufacture of catalyst ink and polymer electrolyte membranes foruse in fuel cells or other electrolytic cells. A membrane electrodeassembly (MEA) is the central element of a proton exchange membrane fuelcell, such as a hydrogen fuel cell. Fuel cells are electrochemical cellswhich produce usable electricity by the catalyzed combination of a fuelsuch as hydrogen and an oxidant such as oxygen. Typical MEA's comprise apolymer electrolyte membrane (PEM) (also known as an ion conductivemembrane (ICM)), which functions as a solid electrolyte. One face of thePEM is in contact with an anode electrode layer and the opposite face isin contact with a cathode electrode layer. Each electrode layer includeselectrochemical catalysts, typically including platinum metal. Gasdiffusion layers (GDL's) facilitate gas transport to and from the anodeand cathode electrode materials and conduct electrical current. The GDLmay also be called a fluid transport layer (FTL) or a diffuser/currentcollector (DCC). The anode and cathode electrode layers may be appliedto GDL's in the form of a catalyst ink, and the resulting coated GDL'ssandwiched with a PEM to form a five-layer MEA. Alternately, the anodeand cathode electrode layers may be applied to opposite sides of the PEMin the form of a catalyst ink, and the resulting catalyst-coatedmembrane (CCM) sandwiched with two GDL's to form a five-layer MEA.Details concerning the preparation of catalyst inks and their use inmembrane assemblies can be found, for example, in U.S. Pat. Publ. No.2004/0107869 (Velamakanni et al.). In atypical PEM fuel cell, protonsare formed at the anode via hydrogen oxidation and transported acrossthe PEM to the cathode to react with oxygen, causing electrical currentto flow in an external circuit connecting the electrodes. The PEM formsa durable, non-porous, electrically non-conductive mechanical barrierbetween the reactant gases, yet it also passes H⁺ ions readily.

The copolymer of the present disclosure may be useful for making acatalyst ink composition. In some embodiments, the copolymer (e.g., as acomponent of the fluoropolymer dispersion described above) can becombined with catalyst particles (e.g., metal particles orcarbon-supported metal particles). A variety of catalysts may be useful.Typically, carbon-supported catalyst particles are used. Typicalcarbon-supported catalyst particles are 50% to 90% carbon and 10% to 50%catalyst metal by weight, the catalyst metal typically comprisingplatinum for the cathode and platinum and ruthenium in a weight ratio of2:1 for the anode. However, other metals may be useful, for example,gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt,nickel, chromium, tungsten, manganese, vanadium, and alloys thereof. Tomake an MEA or CCM, catalyst ink may be applied to the PEM by anysuitable means, including both hand and machine methods, including handbrushing, notch bar coating, fluid bearing die coating, wire-wound rodcoating, fluid bearing coating, slot-fed knife coating, three-rollcoating, or decal transfer. Coating may be achieved in one applicationor in multiple applications. Advantageously, copolymers according to thepresent disclosure may be useful for making a catalyst layer with onecoating application. The catalyst ink may be applied to a PEM or a GDLdirectly, or the catalyst ink may be applied to a transfer substrate,dried, and thereafter applied to the PEM or to the FTL as a decal.

In some embodiments, the catalyst ink includes the copolymer disclosedherein at a concentration of at least 10, 15, or 20 percent by weightand up to 30 percent by weight, based on the total weight of thecatalyst ink. In some embodiment, the catalyst ink includes the catalystparticles in an amount of at least 10, 15, or 20 percent by weight andup to 50, 40, or 30 percent by weight, based on the total weight of thecatalyst ink. The catalyst particles may be added to the fluoropolymerdispersion made as described above in any of its embodiments. Theresulting catalyst ink may be mixed, for example, with heating. Thepercent solid in the catalyst ink may be selected, for example, toobtain desirable rheological properties. Examples of suitable organicsolvents useful for including in the catalyst ink include, loweralcohols (e.g., methanol, ethanol, isopropanol, n-propanol), polyols(e.g., ethylene glycol, propylene glycol, glycerol), ethers (e.g.,tetrahydrofuran and dioxane), diglyme, polyglycol ethers, etheracetates, acetonitrile, acetone, dimethylsulfoxide (DMSO), N,Ndimethyacetamide (DMA), ethylene carbonate, propylene carbonate,dimethylcarbonate, diethylcarbonate, N,N-dimethylformamide (DMF),N-methylpyrrolidinone (NMP), dimethylimidazolidinone, butyrolactone,hexamethylphosphoric triamide (HMPT), isobutyl methyl ketone, sulfolane,and combinations thereof. In some embodiments, the catalyst ink contains0% to 50% by weight of a lower alcohol and 0% to 20% by weight of apolyol. In addition, the ink may contain 0% to 2% of a suitabledispersant.

In some embodiments, the copolymer of the present disclosure may beuseful as a polymer electrolyte membrane. The copolymer may be formedinto a polymer electrolyte membrane by any suitable method, includingcasting, molding, and extrusion. Typically, the membrane is cast from afluoropolymer dispersion (e.g., those described above in any of theirembodiments) and then dried, annealed, or both. The copolymer may becast from a suspension. Any suitable casting method may be used,including bar coating, spray coating, slit coating, and brush coating.After forming, the membrane may be annealed, typically at a temperatureof 120° C. or higher, more typically 130° C. or higher, most typically150° C. or higher. In some embodiments of the method according to thepresent disclosure, a polymer electrolyte membrane can be obtained byobtaining the copolymer in a fluoropolymer dispersion, optionallypurifying the dispersion by ion-exchange purification, and concentratingthe dispersion to make a membrane. Typically, if the fluoropolymerdispersion is to be used to form a membrane, the concentration ofcopolymer is advantageously high (e.g., at least 20, 30, or 40 percentby weight). Often a water-miscible organic solvent is added tofacilitate film formation. Examples of water-miscible solvents include,lower alcohols (e.g., methanol, ethanol, isopropanol, n-propanol),polyols (e.g., ethylene glycol, propylene glycol, glycerol), ethers(e.g., tetrahydrofuran and dioxane), ether acetates, acetonitrile,acetone, dimethylsulfoxide (DMSO), N,N dimethyacetamide (DMA), ethylenecarbonate, propylene carbonate, dimethylcarbonate, diethylcarbonate,N,N-dimethylformamide (DMF), N-methylpyrrolidinone (NMP),dimethylimidazolidinone, butyrolactone, hexamethylphosphoric triamide(HMPT), isobutyl methyl ketone, sulfolane, and combinations thereof.

The present disclosure provides a membrane electrode assembly comprisingat least one of a catalyst ink comprising the copolymer of the presentdisclosure or a polymer electrolyte membrane comprising the copolymer ofthe present disclosure. In some embodiments, both the polymerelectrolyte membrane and catalyst ink comprise embodiments of thecopolymer disclosed herein. The catalyst ink and polymer electrolytemembrane may use the same or different copolymers. In some embodiments,the catalyst ink comprises the copolymer of the present disclosure, andthe polymer electrolyte membrane includes a conventional copolymer(e.g., one that does not include one or more divalent unitsindependently represented by formula:

In some embodiments, the polymer electrolyte membrane is prepared fromthe copolymer of the present disclosure, and the catalyst ink includes aconventional copolymer (e.g., one that does not include one or moredivalent units independently represented by formula:

In some embodiments of the polymer electrolyte membrane of the presentdisclosure, a salt of at least one of cerium, manganese or ruthenium orone or more cerium oxide or zirconium oxide compounds is added to theacid form of the copolymer before membrane formation. Typically the saltof cerium, manganese, or ruthenium and/or the cerium or zirconium oxidecompound is mixed well with or dissolved within the copolymer to achievesubstantially uniform distribution.

The salt of cerium, manganese, or ruthenium may comprise any suitableanion, including chloride, bromide, hydroxide, nitrate, sulfonate,acetate, phosphate, and carbonate. More than one anion may be present.Other salts may be present, including salts that include other metalcations or ammonium cations. Once cation exchange occurs between thetransition metal salt and the acid form of the ionomer, it may bedesirable for the acid formed by combination of the liberated proton andthe original salt anion to be removed. Thus, it may be useful to useanions that generate volatile or soluble acids, for example chloride ornitrate. Manganese cations may be in any suitable oxidation state,including Mn²⁺, Mn³⁺, and Mn⁴⁺, but are most typically Mn²⁺. Rutheniumcations may be in any suitable oxidation state, including Ru³⁺ and Ru⁴⁺,but are most typically Ru³⁺. Cerium cations may be in any suitableoxidation state, including Ce³⁺ and Ce⁴⁺. Without wishing to be bound bytheory, it is believed that the cerium, manganese, or ruthenium cationspersist in the polymer electrolyte because they are exchanged with H⁺ions from the anion groups of the polymer electrolyte and becomeassociated with those anion groups. Furthermore, it is believed thatpolyvalent cerium, manganese, or ruthenium cations may form crosslinksbetween anion groups of the polymer electrolyte, further adding to thestability of the polymer. In some embodiments, the salt may be presentin solid form. The cations may be present in a combination of two ormore forms including solvated cation, cation associated with bound aniongroups of the polymer electrolyte membrane, and cation bound in a saltprecipitate. The amount of salt added is typically between 0.001 and 0.5charge equivalents based on the molar amount of acid functional groupspresent in the polymer electrolyte, more typically between 0.005 and0.2, more typically between 0.01 and 0.1, and more typically between0.02 and 0.05. Further details for combining an anionic copolymer withcerium, manganese, or ruthenium cations can be found in U.S. Pat. Nos.7,575,534 and 8,628,871, each to Frey et al.

The cerium oxide compound may contain cerium in the (IV) oxidationstate, the (III) oxidation state, or both and may be crystalline oramorphous. The cerium oxide may be, for example, CeO₂ or Ce₂O₃. Thecerium oxide may be substantially free of metallic cerium or may containmetallic cerium. The cerium oxide may be, for example, a thin oxidationreaction product on a metallic cerium particle. The cerium oxidecompound may or may not contain other metal elements. Examples of mixedmetal oxide compounds comprising cerium oxide include solid solutionssuch as zirconia-ceria and multicomponent oxide compounds such as bariumcerate. Without wishing to be bound by theory, it is believed that thecerium oxide may strengthen the polymer by chelating and formingcrosslinks between bound anionic groups. The amount of cerium oxidecompound added is typically between 0.01 and 5 weight percent based onthe total weight of the copolymer, more typically between 0.1 and 2weight percent, and more typically between 0.2 and 0.3 weight percent.The cerium oxide compound is typically present in an amount of less than1% by volume relative to the total volume of the polymer electrolytemembrane, more typically less than 0.8% by volume, and more typicallyless than 0.5% by volume. Cerium oxide may be in particles of anysuitable size, in some embodiments, between 1 nm and 5000 nm, 200 nm to5000 nm, or 500 nm to 1000 nm. Further details regarding polymerelectrolyte membranes including cerium oxide compounds can be found inU.S. Pat. No. 8,367,267 (Frey et al.).

The polymer electrolyte membrane, in some embodiments, may have athickness of up to 90 microns, up to 60 microns, or up to 30 microns. Athinner membrane may provide less resistance to the passage of ions. Infuel cell use, this results in cooler operation and greater output ofusable energy. Thinner membranes must be made of materials that maintaintheir structural integrity in use.

In some embodiments, the copolymer of the present disclosure may beimbibed into a porous supporting matrix, typically in the form of a thinmembrane having a thickness of up to 90 microns, up to 60 microns, or upto 30 microns. Any suitable method of imbibing the polymer into thepores of the supporting matrix may be used, including overpressure,vacuum, wicking, and immersion. In some embodiments, the copolymer isembedded in the matrix upon crosslinking. Any suitable supporting matrixmay be used. Typically the supporting matrix is electricallynon-conductive. Typically, the supporting matrix is composed of afluoropolymer, which is more typically perfluorinated. Typical matricesinclude porous polytetrafluoroethylene (PTFE), such as biaxiallystretched PTFE webs. In another embodiment fillers (e.g. fibers) mightbe added to the polymer to reinforce the membrane.

To make an MEA, GDL's may be applied to either side of a CCM by anysuitable means. Any suitable GDL may be used in the practice of thepresent disclosure. Typically the GDL is comprised of sheet materialcomprising carbon fibers. Typically the GDL is a carbon fiberconstruction selected from woven and non-woven carbon fiberconstructions. Carbon fiber constructions which may be useful in thepractice of the present disclosure may include Toray™ Carbon Paper,SpectraCarb™ Carbon Paper, AFN™ non-woven carbon cloth, and Zoltek™Carbon Cloth. The GDL may be coated or impregnated with variousmaterials, including carbon particle coatings, hydrophilizingtreatments, and hydrophobizing treatments such as coating withpolytetrafluoroethylene (PTFE).

In use, the MEA according to the present disclosure is typicallysandwiched between two rigid plates, known as distribution plates, alsoknown as bipolar plates (BPP's) or monopolar plates. Like the GDL, thedistribution plate is typically electrically conductive. Thedistribution plate is typically made of a carbon composite, metal, orplated metal material. The distribution plate distributes reactant orproduct fluids to and from the MEA electrode surfaces, typically throughone or more fluid-conducting channels engraved, milled, molded orstamped in the surface(s) facing the MEA(s). These channels aresometimes designated a flow field. The distribution plate may distributefluids to and from two consecutive MEA's in a stack, with one facedirecting fuel to the anode of the first MEA while the other facedirects oxidant to the cathode of the next MEA (and removes productwater), hence the term “bipolar plate.” Alternately, the distributionplate may have channels on one side only, to distribute fluids to orfrom an MEA on only that side, which may be termed a “monopolar plate.”A typical fuel cell stack comprises a number of MEA's stackedalternately with bipolar plates.

Another type of electrochemical device is an electrolysis cell, whichuses electricity to produce chemical changes or chemical energy. Anexample of an electrolysis cell is a chlor-alkali membrane cell whereaqueous sodium chloride is electrolyzed by an electric current betweenan anode and a cathode. The electrolyte is separated into an anolyteportion and a catholyte portion by a membrane subject to harshconditions. In chlor-alkali membrane cells, caustic sodium hydroxidecollects in the catholyte portion, hydrogen gas is evolved at thecathode portion, and chlorine gas is evolved from the sodiumchloride-rich anolyte portion at the anode. The copolymer of the presentdisclosure may be useful, for example, in the manufacture of catalystink and electrolyte membranes for use in chlor-alkali membrane cells orother electrolytic cells.

The copolymer according to the present disclosure may also be useful hasa binder for an electrode in other electrochemical cells (for example,lithium ion batteries). To make electrodes, powdered active ingredientscan be dispersed in a solvent with the copolymer and coated onto a metalfoil substrate, or current collector. The resulting composite electrodecontains the powdered active ingredient in the polymer binder adhered tothe metal substrate. Useful active materials for making negativeelectrodes include alloys of main group elements and conductive powderssuch as graphite. Examples of useful active materials for making anegative electrode include oxides (tin oxide), carbon compounds (e.g.,artificial graphite, natural graphite, soil black lead, expandedgraphite, and scaly graphite), silicon carbide compounds, silicon-oxidecompounds, titanium sulfides, and boron carbide compounds. Useful activematerials for making positive electrodes include lithium compounds, suchas Li_(4/3)Ti_(5/3)O₄, LiV₃O₈, LiV₂O₅, LiCo_(0.2)Ni_(0.8)O₂, LiNiO₂,LiFePO₄, LiMnPO₄, LiCoPO₄, LiMn₂O₄, and LiCoO₂. The electrodes can alsoinclude electrically conductive diluents and adhesion promoters.

Electrochemical cells including the copolymer disclosed herein as abinder can be made by placing at least one each of a positive electrodeand a negative electrode in an electrolyte. Typically, a microporousseparator can be used to prevent the contact of the negative electrodedirectly with the positive electrode. Once the electrodes are connectedexternally, lithiation and delithiation can take place at theelectrodes, generating a current. A variety of electrolytes can beemployed in a lithium-ion cell. Representative electrolytes contain oneor more lithium salts and a charge-carrying medium in the form of asolid, liquid, or gel. Examples of lithium salts include LiPF₆, LiBF₄,LiClO₄, lithium bis(oxalato)borate, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, LiAsF₆,LiC(CF₃SO₂)₃, and combinations thereof. Examples of solid chargecarrying media include polymeric media such as polyethylene oxide,polytetrafluoroethylene, polyvinylidene fluoride, fluorine-containingcopolymers, polyacrylonitrile, combinations thereof, and other solidmedia that will be familiar to those skilled in the art. Examples ofliquid charge carrying media include ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, ethyl methylcarbonate, butylene carbonate, vinylene carbonate, fluoroethylenecarbonate, fluoropropylene carbonate, gamma-butyrolactone, methyldifluoroacetate, ethyl difluoroacetate, dimethoxyethane, diglyme(bis(2-methoxyethyl) ether), tetrahydrofuran, dioxolane, combinationsthereof and other media that will be familiar to those skilled in theart. Examples of charge carrying media gels include those described inU.S. Pat. No. 6,387,570 (Nakamura et al.) and U.S. Pat. No. 6,780,544(Noh). The electrolyte can include other additives (e.g., a cosolvent ora redox chemical shuttle).

The electrochemical cells can be useful as rechargeable batteries andcan be used in a variety of devices, including portable computers,tablet displays, personal digital assistants, mobile telephones,motorized devices (e.g., personal or household appliances and vehicles),instruments, illumination devices (e.g., flashlights) and heatingdevices. One or more of the electrochemical cells can be combined toprovide battery pack.

Some Embodiments of the Disclosure

In a first embodiment, the present disclosure provides a copolymercomprising:

divalent units represented by formula —[CF₂—CF₂]—;

divalent units independently represented by formula:

wherein a is 0 or 1, b is 2 to 8, c is 0 to 2, e is 1 to 8, and each Xis independently F, —NZH, —NZSO₂(CF₂)₁₋₆SO₂X′,—NZ[SO₂(CF₂)_(d)SO₂NZ]₁₋₁₀SO₂(CF₂)_(d)SO₂X′, or —OZ, wherein Z isindependently a hydrogen, an alkyl group having up to four carbon atoms,an alkali-metal cation or a quaternary ammonium cation, X′ isindependently —NZH or —OZ, and each d is independently 1 to 6; and

one or more divalent units independently represented by formula:

wherein Rf is a linear or branched perfluoroalkyl group having from 1 to8 carbon atoms and optionally interrupted by one or more —O— groups, zis 1 or 2, each n is independently from 1, 3, or 4, m is 0 or 1, m′ is 0or 1, and Rf₁ is a branched perfluoroalkyl group having from 3 to 8carbon atoms, with the proviso that if z is 2, one n may also be 2, withthe proviso that if a is 1, n may also be 2, and with the furtherproviso that when m′ is 1, Rf₁ is a branched perfluoroalkyl group havingfrom 3 to 8 carbon atoms or a linear perfluoroalkyl group having 5 to 8carbon atoms.

In a second embodiment, the present disclosure provides a copolymercomprising: divalent units represented by formula [CF₂—CF₂]—;

divalent units independently represented by formula:

wherein a is 0 or 1, b is 2 to 8, c is 0 to 2, e is 1 to 8, and each X′″is independently —NZH, —NZSO₂(CF₂)₁₋₆SO₂X′, or—NZ[SO₂(CF₂)_(d)SO₂NZ]₁₋₁₀SO₂(CF₂)_(d)SO₂X′, wherein Z is a hydrogen, analkali-metal cation or a quaternary ammonium cation, X′ is independently—NZH or —OZ and each d is independently 1 to 6; and

one or more other fluorinated divalent units independently representedby formula:

wherein Rf is a linear or branched perfluoroalkyl group having from 1 to8 carbon atoms and optionally interrupted by one or more —O— groups, zis 1 or 2, each n is independently from 1 to 4, m is 0 or 1, m′ is 0 or1, and Rf₁ is a branched perfluoroalkyl group having from 3 to 8 carbonatoms, with the proviso that when m′ is 1, Rf₁ is a branchedperfluoroalkyl group having from 3 to 8 carbon atoms or a linearperfluoroalkyl group having 5 to 8 carbon atoms.

In a third embodiment, the present disclosure provides the copolymer ofthe first or second embodiment, wherein b is 2 or 3, c is 0 or 1, and eis 2 or 4.

In a fourth embodiment, the present disclosure provides the copolymer ofany one of the first to third embodiments, wherein when a is 0, then nis not 3.

In a fifth embodiment, the present disclosure provides the copolymer ofany one of the first to fourth embodiments, wherein when a and c are 0,then e is not 2.

In a sixth embodiment, the present disclosure provides the copolymer ofany one of the first to fifth embodiments, wherein at least one n is 1.

In a seventh embodiment, the present disclosure provides the copolymerof any one of the first to sixth embodiments, further comprising atleast one of divalent units derived from chlorotrifluoroethylene ordivalent units derived from hexafluoropropylene.

In an eighth embodiment, the present disclosure provides the copolymerof any one of the first to seventh embodiments, wherein the copolymercomprises the divalent units independently represented by formula

and wherein at least one of a is 1 or m is 1.

In a ninth embodiment, the present disclosure provides the copolymer ofany one of the first to eighth embodiments, further comprising divalentunits independently represented by formula:

wherein p is 0 or 1, q is 2 to 8, r is 0 to 2, s is 1 to 8, and Z′ is ahydrogen, an alkyl group having up to four carbon atoms, an alkali-metalcation or a quaternary ammonium cation.

In a tenth embodiment, the present disclosure provides the copolymer ofany one of the first to ninth embodiments, wherein the divalent unitscomprise at least 60 mole % of [CF₂—CF₂]—, based on the total amount ofdivalent units in the copolymer.

In an eleventh embodiment, the present disclosure provides the copolymerof any one of the first to tenth embodiments, further comprisingdivalent units are derived from bisolefins represented by formulaX₂C═CY—(CW₂)_(m)—(O)_(n)—R_(F)—(O)_(o)—(CW₂)_(p)—CY═CX₂, wherein each ofX, Y, and W is independently fluoro, hydrogen, alkyl, alkoxy,polyoxyalkyl, perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxyalkyl,m and p are independently an integer from 0 to 15, and n, o areindependently 0 or 1.

In a twelfth embodiment, the present disclosure provides the copolymerof the eleventh embodiment, wherein X, Y, and W are each independentlyfluoro, CF₃, C₂F₅, C₃F₇, C₄F₉, hydrogen, CH₃, C₂H₅, C₃H₇, C₄H₉.

In a thirteenth embodiment, the present disclosure provides thecopolymer of any one of the first to twelfth embodiments, wherein atleast a portion of X groups are —OZ.

In a fourteenth embodiment, the present disclosure provides thecopolymer of any one of the first to thirteenth embodiments, wherein Zis an alkali metal cation.

In a fifteenth embodiment, the present disclosure provides the copolymerof any one of the first to twelfth embodiments, wherein Z is hydrogen.

In a sixteenth embodiment, the present disclosure provides the copolymerof any one of the first to fifteenth embodiments, wherein the copolymerhas an —SO₂X equivalent weight in a range from 300 to 2000.

In a seventeenth embodiment, the present disclosure provides thecopolymer of the sixteenth embodiment, wherein the copolymer has an—SO₂X equivalent weight greater than 1000.

In an eighteenth embodiment, the present disclosure provides thecopolymer of any one of the first to seventeenth embodiments, wherein atleast a portion of X groups are —NZH groups.

In a nineteenth embodiment, the present disclosure provides thecopolymer of any one of the first to eighteenth embodiments, furthercomprising divalent units derived from at least one of ethylene,propylene, isobutylene, ethyl vinyl ether, vinyl benzoate, ethyl allylether, cyclohexyl allyl ether, norbomadiene, crotonic acid, an alkylcrotonate, acrylic acid, an alkyl acrylate, methacrylic acid, an alkylmethacrylate, or hydroxybutyl vinyl ether.

In a twentieth embodiment, the present disclosure provides the copolymerof any one of the first to nineteenth embodiments, wherein the copolymerhas up to 100 —COOM and —COF end groups per 10⁶ carbon atoms, wherein Mis independently an alkyl group, a hydrogen atom, a metallic cation, ora quaternary ammonium cation.

In a twenty-first embodiment, the present disclosure provides thecopolymer of any one of the first to twentieth embodiments, wherein thecopolymer has a glass transition temperature of up to 20° C.

In a twenty-second embodiment, the present disclosure provides thecopolymer of any one of the first to twenty-first embodiments, whereinthe copolymer has an alpha transition temperature [T(α)] of at least100° C.

In a twenty-third embodiment, the present disclosure provides thecopolymer of any one of the first to twenty-first embodiments, whereinthe copolymer has a T(α) of up to 100° C. or less than 100° C.

In a twenty-fourth embodiment, the present disclosure provides thecopolymer of any one of the first to twenty-third embodiments, whereinat least one of c is 1 or 2 ore is 3 to 8.

In a twenty-fifth embodiment, the present disclosure provides thecopolymer of any one of the first to twenty-fourth embodiments, whereinthe divalent units independently represented by formula

are present at up to 20 or up to 15 mole percent, or in a range from 3to 20 or 4 to 15 mole percent, based on the total moles of divalentunits in the copolymer.

In a twenty-sixth embodiment, the present disclosure provides thecopolymer of any one of the first to twenty-fifth embodiments, whereinthe divalent units independently represented by formula

are present at up to 30 or up to 25 mole percent, or in a range from 10to 30 or 15 to 25 mole percent, based on the total moles of divalentunits in the copolymer.

In a twenty-seventh embodiment, the present disclosure provides apolymer electrolyte membrane comprising the copolymer of any one of thefirst to twenty-sixth embodiments.

In a twenty-eighth embodiment, the present disclosure provides thepolymer electrolyte membrane of the twenty-seventh embodiment, whereinthe polymer electrolyte membrane further comprises at least one ofcerium cations, manganese cations, ruthenium cations, or a cerium oxide.

In a twenty-ninth embodiment, the present disclosure provides thepolymer electrolyte membrane of the twenty-eighth embodiment, whereinthe at least one of cerium cations, manganese cations, or rutheniumcations are present in a range from 0.2 to 20 percent relative to theamount of sulfonate groups in the copolymer.

In a thirtieth embodiment, the present disclosure provides a catalystink comprising the copolymer of any one of the first to twenty-sixthembodiments.

In a thirty-first embodiment, the present disclosure provides a membraneelectrode assembly comprising at least one of the polymer electrolytemembrane of any one of the twenty-seventh to twenty-ninth embodiments orthe catalyst ink of the thirtieth embodiment.

In a thirty-second embodiment, the present disclosure provides a binderfor an electrode comprising the copolymer of any one of the first totwenty-sixth embodiments.

In a thirty-third embodiment, the present disclosure provides anelectrochemical cell comprising the binder of the thirty-secondembodiment.

In a thirty-fourth embodiment, the present disclosure provides a methodof making the copolymer of any one of first to twenty-sixth embodiments,the method comprising copolymerizing components comprisingtetrafluoroethylene, a compound independently represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—O—(C_(e)F_(2e))—SO₂X″, and at leastone perfluoroalkoxyalkyl vinyl ether, perfluoroalkoxyalkyl allyl ether,perfluoroalkylvinyl ether, or perfluoroalkyl allyl ether, wherein b is 2to 8, c is 0 to 2, e is 1 to 8, and X″ is —F, —NZH or —OZ, wherein Z isa hydrogen, methyl, an alkali-metal cation, or a quaternary ammoniumcation.

In a thirty-fifth embodiment, the present disclosure provides the methodof the thirty-fourth embodiment, wherein copolymerizing is carried outby aqueous emulsion polymerization.

In a thirty-sixth embodiment, the present disclosure provides the methodof the thirty-fourth or thirty-fifth embodiment, wherein thecopolymerizing is carried out at a pH higher than 8.

In a thirty-seventh embodiment, the present disclosure provides themethod of any one of the thirty-fourth to thirty-sixth embodiments,wherein copolymerizing is carried out in the presence of a bisulfate orsulfite salt to generate —SO₂X end groups, wherein X is independently—NZH or —OZ, wherein each Z is independently a hydrogen, methyl, analkali-metal cation or a quaternary ammonium cation.

In a thirty-eighth embodiment, the present disclosure provides themethod of any one of the thirty-fourth to thirty-seventh embodiments,wherein the copolymerizing is carried out in the absence of afluorinated emulsifier.

In a thirty-ninth embodiment, the present disclosure provides the methodof any one of the thirty-fourth to thirty-eighth embodiments, whereinthe copolymer comprises anionic species that are not covalently bound tothe ionomer, the method further comprising contacting a dispersion ofthe copolymer with an anion exchange resin having associated hydroxideions, and exchanging at least a portion of the anionic species with thehydroxide ions to provide an anionic exchanged dispersion.

In a fortieth embodiment, the present disclosure provides the method ofany one of the thirty-fourth to thirty-ninth embodiments, wherein thecopolymer comprises cationic species that are not covalently bound tothe copolymer, the method further comprising contacting a dispersion ofthe copolymer with a cation exchange resin having acidic protons, andexchanging at least a portion of the cationic species with the protonsto provide cation-exchanged dispersion.

In a forty-first embodiment, the present disclosure provides the methodof any one of the thirty-fourth to fortieth embodiments, furthercomprising spray drying the copolymer.

In a forty-second embodiment, the present disclosure provides the methodof any one of the thirty-fourth to forty-first embodiments, furthercomprising post-fluorinating the copolymer.

In a forty-third embodiment, the present disclosure provides a method ofthe forty-second embodiment, further comprising treating thepost-fluorinated copolymer with ammonia to provide —SO₂—NH₂ groups onthe copolymer.

In a forty-fourth embodiment, the present disclosure provides the methodof the forty-third embodiment, further comprising treating the copolymerwith a disulfonyl fluoride or disulfonyl chloride.

In order that this disclosure can be more fully understood, thefollowing examples are set forth. It should be understood that theseexamples are for illustrative purposes only and are not to be construedas limiting this disclosure in any manner.

EXAMPLES

All materials are commercially available, for example from Sigma-AldrichChemical Company; Milwaukee, Wis., or known to those skilled in the artunless otherwise stated or apparent. The following abbreviations areused in this section: L=liters, mL=milliliters, g=grams, min=minutes,rpm=revolutions per minute, sec=seconds, h=hours, mol=moles, mol %=molepercent, wt %=weight percent, nm=nanometer, gm=micrometer,mm=millimeter, cm=centimeter, ppm=parts per million, NMR=nuclearmagnetic resonance, ° C.=degrees Celsius, kPa=kiloPascal, mW=milliWatt,kcps=thousand counts per second.

Results were obtained using the following test methods, unless otherwisenoted.

Solid Content

Solid content was determined gravimetrically by placing samples of thedispersions on a heated balance and recording the mass before and afterevaporation of solvent. The solid content was the ratio of the initialmass of the sample and the mass of the sample when the mass did notdecrease further with continued heating.

Equivalent Weight (EW)

The EW of a copolymer of TFE, a sulfonyl fluoride monomer (M2), and avinyl ether or allyl ether monomer (M3) can be calculated by theformula:

${EW} = {\left( \frac{\left( {{{mol}\mspace{14mu}\%\mspace{14mu}{TFE}} + {\left( \frac{{molar}\mspace{14mu}{mass}\mspace{14mu}{M3}}{{molar}\mspace{14mu}{mass}\mspace{14mu}{TFE}} \right) \times {mol}\mspace{14mu}\%\mspace{14mu} M\; 3}} \right)}{{{mol}\mspace{14mu}\%\mspace{14mu} M\; 2} + {{molar}\mspace{14mu}{mass}\mspace{14mu} M\; 2}} \right) \times 100}$Copolymer Composition

¹⁹F-NMR spectra were used to determine the composition of the purifiedpolymers. An NMR spectrometer available under the trade designationAVANCE II 300 from Broker, Billerica, Mass., USA with a 5 mm Broadbandprobe was used. Samples of about 13 weight percent polymer dispersionwere measured at 60° C.

Determination of Carboxyl Endgroups

A Fourier transform infrared spectroscopy (FT-IR) measurement can usedto determine the number of carboxyl endgroups per 10⁶C-atoms in thecopolymer. The measurement is performed by FT-IR in a transmissiontechnique. The measured sample has a film thickness of 100 μm. The wavenumbers of the COOH peaks of interest are 1776 cm⁻¹ and 1807 cm⁻¹. Thewave number of the C(0)F peak is 1885 cm⁻¹. (C(O)F will convert to acarboxyl group). To quantify the amount of carboxyl (C(O)F) endgroups ofthe polymer two IR spectra are taken. One from the carboxyl containingsample and one from a reference sample (without carboxyl groups).

The number of endgroups per 10⁶ carbon atoms can be calculated viaequation 1, 2 and 3 for F₁, F₂ and F₃:(peak high×F₁)/film thickness [mm]  (1)(peak high×F₂)/film thickness [mm]  (2)(peak high×F₃)/film thickness [mm]  (3)withF₁: calculated factor related to the reference spectrum and ν=1776 cm⁻¹F₂: calculated factor related to the reference spectrum and ν=1807 cm⁻¹F₃: calculated factor related to the reference spectrum and ν=1885 cm⁻¹The sum of the results from the equations 1 to 3 yield the number ofcarboxyl endgroups per 10⁶ carbon atoms.Particle Size by Dynamic Light Scattering

The particle size determination was conducted by dynamic lightscattering according to ISO 13321 (1996). A Zeta Sizer Nano ZS,available from Malvern Instruments Ltd, Malvern, Worcestershire, UK,equipped with a 50 mW laser operating at 532 nm was used for theanalysis. 12 mm square glass cuvettes with round aperture and cap (PCS8501, available from Malvern Instruments Ltd) were used to mount asample volume of 1 mL. Since light scattering of surfactants isextremely sensitive to the presence of larger particles, e.g. dustparticles, the presence of contaminants was minimized by thoroughlycleaning the cuvettes before the measurements. The cuvettes were washedwith freshly-distilled acetone for 8 h in a cuvette washing device. Dustdiscipline was also applied to the samples by centrifuging thesurfactant solutions in a laboratory centrifuge at 14,500 G (142,196N/kg) for 10 min prior to the measurements. The measuring device wasoperated at 25° C. in 173° backscattering mode. Low correlation times oft<1⁻⁶ sec were enabled by the research tool (the research tool is asoftware up-grade of the standard instrument provided by the supplier).In order to exploit the complete scattering ability of the samplevolume, the following settings were applied in all cases: “attenuator,”11; “measurement position,” 4.65 mm (center of the cell). Under theseconditions, the baseline scattering of pure water (reference) is around250 kcps. Each measurement consisting of 10 sub-runs was repeated forfive times. The particle sizes are expressed as D₅₀ value.

Melt Flow Index

The melt flow index (MFI), reported in g/10 min, was measured with aGoettfert MPD, MI-Robo, MI4 melt indexer (Buchen, Germany) following asimilar procedure to that described in DIN EN ISO 1133-1 at a supportweight of 5.0 kg and a temperature of 265° C. The MFI was obtained witha standardized extrusion die of 2.1 mm in diameter and a length of 8.0mm.

T(α) Measurement

A TA Instruments AR2000 EX rheometer was used to measure the T(α) of thepolymer samples. Samples were heated on a temperature ramp from −100° C.to about 125° C. at 2° C. per minute. Measurements were made at afrequency of one hertz.

Glass Transition Temperature

A TA Instruments Q2000 DSC was used to measure the glass transitiontemperature (Tg) of the polymer samples. Samples were heated on atemperature ramp from −50° C. to about 200° C. at 10° C. per minute.Transition temperatures were analyzed on the second heats.

Oxygen Permeability

The oxygen permeability as a function of temperature for each membranewas determined using the time lag method. The membranes with an activearea of 1 cm² were placed in a permeability cell. Both chambers of thecell were subsequently evacuated for 6 hours. Time zero for the testcoincided with the pressurization of upper chamber to 760 cm Hg with thechallenging gas (oxygen). The variation of the pressure as a function oftime in the evacuated lower chamber was measured using a pressure sensor(Baratron®, MKS, MA, USA) with a sensitivity of 10⁻³ cm Hg.

The oxygen permeability P in barrer (cm³ _(stp) cm/sec cm² cm Hg) wascalculated using the following expression:P=[V _(b)1/ATRp _(a)]dp _(b) /dtwhere V_(b) is the volume of the lower chamber in cm³, 1 is the membranethickness in cm, A the exposed surface area of the membrane in cm², T istemperature in ° K, p_(a) is the pressure of the upper chamber in cm Hg,R is the gas constant (6236.367 cm Hg cm³/mol ° K), and dp_(b)/dt is therate of change of the pressure in the lower chamber as a function oftime measured in the linear part of the pressure—time curve (cm Hg/sec).

Example 1 (EX-1)

A polymer of tetrafluoroethylene (TFE), F₂C═CF—O—CF₂CF₂CF₂CF₂SO₂F(MV4S), and CF₂═CF—O—(CF₂)₃—OCF3 (MV31) was prepared:

MV4S was prepared according to the method described in U.S. Pat. No.6,624,328 (Guerra). MV31 was prepared according to the method describedin U.S. Pat. No. 6,255,536 (Worm et al.)

A 4-L polymerization kettle equipped with an impeller agitator systemwas charged with ammonium oxalate monohydrate (5 g) and oxalic aciddihydrate (1 g) in H₂O (2000 g) and 40 g of a 30 wt. % aqueous solutionof CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄, prepared as described in “Preparationof Compound 11” in U.S. Pat. No. 7,671,112. The kettle was degassed andsubsequently charged with nitrogen several times to assure that all ofoxygen was removed. Afterwards, the kettle was purged with TFE. Thekettle was then heated to 50° C. and the agitation system was set to 320rpm. A mixture of MV4S (260 g), MV31 (50 g), and 8.6 g of the 30 wt. %CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄ solution and deionized water (165 g) wereemulsified under high shear by an agitator available under the tradedesignation “ULTRA-TURRAX 150” from IKA Works, Wilmington, N.C., USAoperated at 24000 rpm for 2 min. The MV4S and MV31 emulsion was chargedinto the reaction kettle. The kettle was further charged with TFE (127g) to a pressure of 6 bar (600 kPa). The polymerization was initiated bya 0.045% solution of KMnO₄ (33 g) in deionized water. As the reactionstarted, the reaction temperature of 50° C. as well as the reactionpressure of 6 bar (600 kPa) were maintained by feeding TFE into the gasphase. After the first pressure drop, the continuous feeding of the MV4Sand MV31 emulsion (in total 1037 g: 557 g MV4S and 106 g MV31 and 21 gof the 30% CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄ solution in 353 g deionizedwater), TFE (458 g), and of a 0.045% solution of KMnO₄ in deionizedwater (350 g) was continued. The molar ratio of the continuous feed was72 mol % TFE, 23 mol % MV4S and 5 mol % MV31. The average metering rateof the continuous addition of the 0.045% KMnO₄ solution was 92 g/h toobtain a polymer dispersion with a solid content of 23.2%. Thepolymerization time was 228 min. The latex particle diameter was 126 nmaccording to dynamic light scattering.

The polymer dispersion was charged into a 100L glass vessel equippedwith a lab stirrer (PENDRAULIK). While the lab stirrer of the glassvessel was rotated to 2500 rpm, a 65 wt-% nitric acid (170 g) was fedcontinuously in the glass vessel to precipitate the polymer. Then themixture was rotated for 1 h under the same stirring conditions with afinal solid content of 1.4% in the polymerization medium (water phase).

The remaining aqueous polymerization medium was removed and the wetpolymerization crumb was washed seven times with 4 L DI water while thestirrer was rotated to 930 rpm. The pH value of the seventh washingmedium was nearly 4. The wet polymerizate was transferred in twoportions in an air circulation dryer. Each portion was dried for 17hours at 80° C. with a final water content of ≤0.1% determined bythermobalance.

The coagulated, washed, and dried polymer had a MFl (265° C./5 kg) of 41g/10 min. The polymer had a composition of 70.3 mol % TFE, 24.4 mol-%MV4S and 5.3 mol % MV31 as determined by ¹⁹F-NMR-spectroscopy. Thiscorresponds to an equivalent weight EW of 740. The glass transitiontemperature (Tg) was measured using the test method described above andfound to be 3° C.

Hydrolysis of the polymer was done in a Parr 4554 2-Gallon Floor StandReactor equipped with a Parr 4848 Reactor Controller, 2700W Heater, aParr Magnetic Drive Mixer, and a Neslab Thermoflex 2500 chiller forcooling. The reactor was charged with 1.5 L of deionized (DI) water, 24g of LiOH*H₂O, 14.1 g of Li₂CO₃, and 141 g of the polymer. The vesselwas sealed, and the mixer was set to 300 rpm. The reactor was thenheated to 255° C. over a period of 111 minutes. This temperature washeld for 60 minutes. It was then cooled to 25° C. over 23 minutes, andupon reaching this temperature the mixer was shut off The dispersion wasdrained from the reactor into 4 L HDPE bottles and allowed to restovernight.

The dispersion was passed through an ion exchange bed consisting of aKimble Chromaflex Column with the dimensions of 38×500 mm filled with300 mL of Amberlite IR-120(Plus) Hydrogen Form Ion Exchange Resin. Theresin was prepared by first flushing the column with 3 L of DI waterwith the stop cock completely open. After 900 mL of 5% HCl solution waspassed through the column over 30 minutes followed by 600 mL of DI waterover 20 minutes. Next 3 L of DI water was passed through with the stopcock fully open. The dispersion was then ion exchanged at a rate of 1200mL per hour. Any precipitate that formed after hydrolysis was not fedinto the ion exchange column. The resin was regenerated after every 400mL of dispersion using the same process outlined above.

To dry the ionomer and prepare solvent and water based dispersions, 20to 25 mL of the ion exchanged dispersion was placed into a 40-mL HDPEbottle. The open bottle was placed in a muffle furnace set to 70° C.where it remained for 20 to 24 hours until the moisture content droppedbelow 10%, and the ionomer was a friable solid. Once the dispersion haddried, the final moisture content was determined, and n-propanol and DIH₂O with 18.2 MOhm-cm resistivity were added. In this example 1.96 g ofionomer was combined with 4.32 g of n-propanol and 2.72 g of H₂O toachieve a dispersion consisting of 20% ionomer, 48% n-propanol, and 32%water. The bottle was then placed on a roller set to 45 to 65 rpm for aperiod of 24 hours. A clear dispersion was formed with no visibleundispersed material.

To make a membrane, dispersion was concentrated by rotary evaporation tonear solids and then exposed to a stream of nitrogen gas. The driedionomer was dispersed at 28-30 wt % into a 60/40 blend of n-propanol andwater at room temperature. The solution was coated onto 2 mil (50.8micrometer) thickness “KAPTON” polyimide liner secured to a glasssubstrate. The film was dried at 120° C. for 30 minutes and thentransferred from the glass substrate to an aluminum pan. Drying wascontinued 140° C. for 15 minutes, ramped to 160° C. for 10 minutes, andthen cooled to room temperature.

The T(α) was measured according to the test method above and determinedto be 98° C.

The membrane was evaluated at 30° C. using the Oxygen Permeabilityevaluation method described above. A value of 161 (barrer×10¹⁰) wasmeasured. The oxygen permeability at 50° C. and 70° C. was found to behigher than the detection limit.

Example 2 (EX-2)

A polymer of tetrafluoroethylene (TFE), F₂C═CF—O—CF₂CF₂CF₂CF₂SO₂F(MV4S), and CF₂═CF—O—(CF₂)₃—OCF₃ (MV31) was prepared:

MV4S and MV31 were prepared as described in Example 1.

A 4-L polymerization kettle equipped with an impeller agitator systemwas charged with ammonium oxalate monohydrate (5 g) and oxalic aciddihydrate (1 g) in H₂O (2000 g) and 40 g of a 30 wt. % aqueous solutionof CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄. The kettle was degassed andsubsequently charged with nitrogen several times to assure that all ofoxygen was removed.

Afterwards, the kettle was purged with TFE, The kettle was then heatedto 50° C. and the agitation system was set to 320 rpm. A mixture of MV4S(237 g), MV31 (78 g), and 9.6 g of the 30 wt. %CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄ solution and deionized water (147 g) wereemulsified under high shear by an agitator available under the tradedesignation “ULTRA-TURRAX T 50” from IKA Works, operated at 24000 rpmfor 2. min. The MV4S and MV31 emulsion was charged into the reactionkettle, The kettle was further charged with TFE (126 g) to a pressure of6 bar (600 kPa). The polymerization was initiated by a 0.045% solutionof KMnO₄ (20 g) in deionized water. As the reaction started, thereaction temperature of 50° C. as well as the reaction pressure of 6 bar(600 kPa) were maintained by feeding TFE into the gas phase. After thefirst pressure drop, the continuous feeding of the MV4S and MV31emulsion (in total 1128 g: 567 g NEWS and 187 g MV31 and 23 g of the 30%CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄-sol anon in 351 g deionized water), TFE(351 g), and of a 0.045% solution of KMnO₄ in deionized water (120 g)was continued. The average metering rate of the continuous addition ofthe 0.045% KMnO₄ solution was 37 g/h to obtain a polymer dispersion witha solid content of 19.7%. The polymerization. time was 194 min. Thelatex particle diameter was 114 nm according to dynamic lightscattering.

The copolymer was coagulated, washed, and dried similarly to Example 1.The coagulated, washed, and dried polymer had a MFI (265° C./5 kg) of 57g/10 min. The calculated equivalent weight EW was 742.

Illustrative Example 3 (Ill. EX-3)

A polymer of tetrafluoroethylene (TFE), F₂C═CF—O—CF₂CF₂CF₂CF₂SO₂F(MV4S), and CF₂═CF—O—(CF₂)₂—CF₃ (PPVE-1) was prepared:

A 4-L polymerization kettle with an impeller agitator system was chargedwith 5 g ammonium oxalate monohydrate and 1 g oxalic acid dihydrate in2000 g H₂O and 40 g of a 30 wt. % aqueous solution ofCF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄. The kettle was degassed and subsequentlycharged with nitrogen several times to assure that all of oxygen wasremoved. Afterwards, the kettle was purged with TFE. The kettle was thenheated to 50° C. and the agitation system was set to 320 rpm. A mixtureof 80 g MV4S, 2.7 g of a 30 wt. % CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄ solutionand 51 g deionized water were emulsified under high shear by a“ULTRA-TURRAX T 50” agitator from IKA Works operated at 24000 rpm for 2min. The MV4S-emulsion was charged into die reaction kettle. The kettlewas further charged with 114 g TM and 40 g PPVE-1 to 6 bar pressure (600kPa). The polymerization was initiated by 16 g of a 0.09% solution ofpotassium permanganate (KMnO₄) in deionized water. As the reactionstarted, the reaction temperature of 50° C. as well as the reactionpressure of 6 bar (600 kPa) was maintained by feeding TFE arid PPVE-1into the gas phase. After the first pressure drop the continuous feedingof 190 g of the MV4S-emulsion (114 g MV4S and 4 g of a 30 wt. %CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄ solution in 72 g deionized water), 193 gTFE, 121 g PPVE-1, and 235 g of a 0.09% solution of KMnO₄ in deionizedwater was continued. The average metering rate of the continuouslyaddition of the 0.09% KMnO₄ solution was 123 g/h to obtain a polymerdispersion with a solid content of 14.1%. The polymerization time was115 mm and latex particle diameter was 150 nm according to dynamic lightscattering.

The copolymer was coagulated, washed, and dried similarly to Example 1.The coagulated, washed, and dried polymer had a MFI (265° C./5 kg) of 66g/10 min. The polymer showed a chemical composition of 74.2 mol-% TFE,16.1 mol-% MV4S and 9.7 mol-% PPVE-1 as determined by¹⁹F-NMR-spectroscopy. This corresponds to an equivalent weight of 1000.The glass transition temperature (Tg) was measured using the test methoddescribed above and found to be 10° C.

The polymer was hydrolyzed similarly to Example 1 except 16.2 g ofLiOH*H₂O, 9.5 g of Li₂CO₃ and 129 g of the polymer was charged into thereactor. The reactor was then heated to 255° C. over a period of 114minutes. The dispersion was ion exchanged, dried, and an n-propanolbased dispersion was prepared similarly to Example 1. In Example 2, 2.14g of ionomer was combined with 4.70 g of n-propanol and 2.96 g DI H₂O. Aclear dispersion was formed with no visible undispersed material.

A membrane was made similarly to Example 1. The T(α) was measuredaccording to the test method above and determined to be 93° C. Themembrane was evaluated at 30° C. using the Oxygen Permeabilityevaluation method described above. A value of 2.6 (barrer×10¹⁰) wasmeasured. The oxygen permeability at 50° C. and 70° C. was found to be5.8 and 10.1 (barrer×10¹⁰), respectively.

Comparative Example A

A polymer of tetrafluoroethylene (TFE) and F₂C═CF—O—CF₂CF₂CF₂CF₂SO₂F(MV4S) was prepared:

MV4S was prepared as described above.

A 4-L polymerization kettle equipped with an impeller agitator systemwas charged with ammonium oxalate monohydrate (5 g) and oxalic aciddihydrate (1 g) in H₂O (2000 g) and 40 g of a 30 wt. % aqueous solutionof CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄. The kettle was degassed andsubsequently charged with nitrogen several times to assure that all ofoxygen was removed. Afterwards, the kettle was purged with TEE. Thekettle was then heated to 50° C. and the agitation system was set to 320rpm. A mixture of MV4S (200 g), 15 g of the 30 wt. %CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄ solution and deionized water (360 g) wereemulsified under high shear by an agitator available under the tradedesignation. “ULTRA-TURRAX T 50” from IKA Works operated at 24000 rpmfor 2 mM. The MV4S emulsion was charged into the reaction kettle. Thekettle was further charged with TFE (115 g) to a pressure of 6 bar (600kPa). The polirierization was initiated by a 0.06% solution of KMnO₄ (13g) in deionized water. As the reaction started, the reaction temperatureof 50° C. as well as the reaction pressure of 6 bar (600 kPa) weremaintained by feeding TFE into the gas phase. After the first pressuredrop, the continuous feeding of the MV4S emulsion (in total 1234 g: 630g MV4S and 24 g of the 30% CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄-solution in 580g deionized water), TFE (450 g), and of a 0.045% solution of KMnO₄ indeionized water (297 g) was continued. The average metering rate of thecontinuous addition of the 0.06% KMnO₄ solution was 80 g/h to obtain apolymer dispersion with a solid content of 22%. The polymerization timewas 232 min. The latex particle diameter was 75 nm according to dynamiclight scattering.

4.1 kg of the polymer dispersion with a solid content of 22% was chargedinto a 10-L glass vessel equipped with a lab stirrer (PENDRAULIK). Whilethe lab stirrer of the glass vessel was rotated to 2500 rpm, a 65 wt-%nitric acid (170 g) was fed continuously in the glass vessel toprecipitate the polymer. Then the mixture was rotated for 1 h under thesame stirring conditions with a final solid content of 1.4% in thepolymerization medium (water phase). The remaining aqueouspolymerization medium was removed and the wet polymerization crumb waswashed seven times with 4 liter DI water while the stirrer was rotatedto 930 rpm. The pH value of the seventh washing medium was nearly 4.

The wet polymerizate was transferred in two portions in an aircirculation dryer. Each portion was dried for 17 hours at 80° C. with afinal water content of ≤0.1% determined by thermobalance. The yield ofdried polymer of the was 840 g.

The copolymer was coagulated, washed, and dried similarly to Example 1.The coagulated, washed, and dried polymer had a MFI (265° C./5 kg) of 38g/10 min. The so-obtained polymer showed a chemical composition of 78mol-% TFE, 22 mol-% MV4S as determined by ¹⁹F-NMR-spectroseopy Thiscorresponds to an equivalent weight of 734.

The polymer was hydrolyzed similarly to Example 1 except the reactor wascharged with 4 L of DI water, 200 g of LiOH*H₂O, 100 g of Li₂CO₃, and1000 g of the polymer. The dispersion was ion exchanged and driedsimilarly to Example 1. A dispersion was prepared similarly toExample 1. The dispersion was clear with no visible undispersedmaterial, however the dispersion was very viscous. To prepare amembrane, another dispersion consisting of 20 wt % solids dispersed inethanol:water at a ratio 55:45 was prepared. A clear dispersion wasformed with no visible undispersed material. The dispersion was coatedsimilarly to Example 1 except the film was dried at 80° C. for 10minutes and then at 200° C. for 15 minutes. The T(α) was measuredaccording to the test method above and determined to be 104° C.

A dispersion consisting of 15 wt % ionomer, 46.75% n-propanol, and38.25% water was prepared similarly to Example 1. A clear dispersion wasformed with no visible undispersed material. A membrane was madesimilarly to Example 1 except the film was dried at 90° C. for 10minutes and then at 100° C. for 15 minutes, and then ramped to 190° C.for 12 minutes, and then cooled to room temperature. The membrane wasevaluated at 30° C. using the Oxygen Permeability evaluation methoddescribed above. A value of 0.64 (barter×10¹⁰) was measured. The oxygenpermeability at 50° C. and 70° C. was found to be 1.4 and 2.8(barrer×10¹⁰), respectively.

Various modifications and alterations of this disclosure may be made bythose skilled in t art without departing from the scope and spirit ofthe disclosure, and it should be understood that this disclosure is notto be unduly limited to the illustrative embodiments set forth herein.

What is claimed is:
 1. A copolymer comprising: divalent unitsrepresented by formula —[CF₂—CF₂]—; divalent units independentlyrepresented by formula:

wherein a is 0 or 1, b is 2 to 8, c is 0 to 2, and e is 1 to 8; and oneor more divalent units independently represented by formula:

wherein Rf is a linear or branched perfluoroalkyl group having from 1 to8 carbon atoms and optionally interrupted by one or more —O— groups, zis 1 or 2, each n is independently 1, 3, or 4, m is 0 or 1, m′ is 0 or1, and Rf₁ is a branched perfluoroalkyl group having from 3 to 8 carbonatoms, with the proviso that if z is 2, n may also be 2, with theproviso that if a is 1, n may also be 2, and with the further provisothat when m′ is 1, Rf₁ is a branched perfluoroalkyl group having from 3to 8 carbon atoms or a linear perfluoroalkyl group having 5 to 8 carbonatoms, wherein the copolymer has an —SO2F equivalent weight in a rangefrom 300 to 2000, wherein the copolymer has a glass transitiontemperature of up to 20° C.
 2. The copolymer of claim 1, wherein b is 2or 3, c is 0 or 1, and e is 2 or
 4. 3. The copolymer of claim 1, with atleast one of the following further provisos: when a is 0, then n is not3, or when a and c are 0, then e is not
 2. 4. The copolymer of claim 1,wherein at least one n is
 1. 5. The copolymer of claim 1, furthercomprising at least one of divalent units derived fromchlorotrifluoroethylene or divalent units derived fromhexafluoropropylene.
 6. The copolymer of claim 1, wherein the copolymercomprises the divalent units independently represented by formula

and wherein at least one of a is 1 or m is
 1. 7. The copolymer of claim1, wherein the divalent units independently represented by formula

are present in a range from 3 to 20 or 4 to 15 mole percent, based onthe total moles of divalent units in the copolymer.
 8. The copolymer ofclaim 1, wherein the copolymer has an — SO₂F equivalent weight greaterthan
 1000. 9. The copolymer of claim 1, wherein at least one of c is 1or 2 or e is 3 to
 8. 10. The copolymer of claim 1, wherein the copolymercomprises the divalent units independently represented by formula

and wherein at least one of a is 1 or m is
 1. 11. The copolymer of claim1, wherein the copolymer is free of divalent units derived fromX₂C═CY-(CW₂)_(m)-(O)_(n)—R_(F)—(O)_(o)-(CW₂)_(p)—CY═CX₂, where each ofX, Y, and W is independently fluoro, hydrogen, alkyl, alkoxy,polyoxyalkyl, perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxyalkyl,m and p are independently an integer from 0 to 15, and n, o areindependently 0 or 1.